Publications

@article{kennedy1988lowb,

title = {Low temperature microwave surface resistance of Y sub (1) Ba sub (2) Cu sub (3) O sub (y) and La sub (1. 85) Sr sub (0. 15) CuO sub (4).},

author = {WL Kennedy and S Sridhar},

year  = {1988},

date = {1988-01-01},

journal = {SOL. ST. COMMUN.},

volume = {68},

number = {1},

pages = {71--75},

abstract = {Measurements of the microwave surface resistance R sub(s) at 9.58 GHz of polycrystalline Y sub(1)Ba sub(2)Cu sub(3)O sub(y) and La sub(1.85)Sr sub(0.15)CuO sub(4) over a wide range in temperature from 4.2 K to 100 K are reported. The temperature dependence of these materials are anomalous, over the entire temperature range, though very similar. R sub(s) is large at all temperatures, gradually decreasing by about 2 orders of magnitude from T sub(c) to 4.2 K. The lowest values measured were R sub(s)(4.2 K) = 4.89 x 10 super(-3) Omega for Y sub(1)Ba sub(2)Cu sub(3)O sub(y) and 1.13 x 10 super(-2) Omega for La sub(1.85)Sr sub(0.15)CuO sub(4). Analysis of R sub(s) for an exponential temperature dependence at low temperatures does not indicate a clear and unique quasiparticle gap.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1987electrodynamic,

title = {Electrodynamic response of Y 1 Ba 2 Cu 3 O y and La 1.85 Sr 0.15 Cu O 4- $delta$ in the superconducting state},

author = {S Sridhar and CA Shiffman and H Hamdeh},

year  = {1987},

date = {1987-01-01},

journal = {Physical Review B},

volume = {36},

number = {4},

pages = {2301},

publisher = {American Physical Society},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{lu1987glassy,

title = {Glassy Yb0. 17Ba0. 33Cu0. 50 alloy as precursor for the high-Tc oxide superconductor Y1Ba2Cu3Ox},

author = {YZ Lu and P Haldar and R Markiewicz and S Sridhar and BC Giessen},

year  = {1987},

date = {1987-01-01},

journal = {Materials Letters},

volume = {5},

number = {10},

pages = {380--383},

publisher = {North-Holland},

abstract = {We describe the preparation by rapid solidification processing (RSP), properties and alloy chemistry of the glassy alloy Yb0.17Ba0.33Cu0.50 and its oxidation to form the superconductor Yb1Ba2Cu3Ox with Tc = 93 K. Processing features and advantages of forming high-Tc superconductors via metallic alloy precursors are discussed.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{lu1987glassyb,

title = {Glassy Yb sub 0. 17 Ba sub 0. 33 Cu sub 0. 50 Alloy as Precursor for the High-T sub c Oxide Superconductor Yb sub 1 Ba sub 2 Cu sub 3 O sub x},

author = {YZ Lu and P Haldar and R Markiewicz and S Sridhar and BC Giessen},

year  = {1987},

date = {1987-01-01},

journal = {Mater. Lett.},

volume = {5},

number = {10},

pages = {380--383},

abstract = {The authors describe the preparation by rapid solidification processing (RSP), properties and alloy chemistry of the glassy alloy Yb/sub 0.17/Ba/sub 0.33/Cu/sub 0.50/and its oxidation to form the superconductor Yb/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/with T/sub c/= 93 K. Processing features and advantages of forming high-T/sub c/superconductors via metallic alloy precursors are discussed. 16 refs.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1987electrodynamicb,

title = {Electrodynamic response of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/and La/sub 1. 85/Sr/sub 0. 15/CuO/sub 4-//sub delta/in the superconducting state},

author = {S Sridhar and CA Shiffman and H Hamdeh},

year  = {1987},

date = {1987-01-01},

journal = {Phys. Rev. B: Condens. Matter;(United States)},

volume = {36},

number = {4},

publisher = {Department of Physics, Northeastern University, Boston, Massachusetts 02115},

abstract = {Measurements of the temperature dependence of the surface resistance R/sub s/at 9.85 GHz and the screening length delta/sub s/at 1 MHz for the superconducting states of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/and La/sub 1.85/Sr/sub 0.15/CuO/sub 4/show strong correlations, suggesting that the superconducting state is the same in the two materials. While the overall temperature dependence of R/sub s/is reasonably well described by the Bardeen-Cooper-Schrieffer (BCS) theory in the very dirty limit, additional features are seen in R/sub s/and also in delta/sub s/which suggest detailed deviations from the BCS s-wave state.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1987electrodynamicc,

title = {Electrodynamic response of Y1Ba2Cu3Oy and La1. 85Sr0. 15CuO4-delta in the superconducting state},

author = {S Sridhar and CA Shiffman and H Hamdeh},

year  = {1987},

date = {1987-01-01},

journal = {Physical Review B},

volume = {36},

pages = {2301--2304},

abstract = {Measurements of the temperature dependence of the surface resistance R s at 9.85 GHz and the screening length delta s at 1 MHz for the superconducting states of Y 1 Ba 2 Cu 3 O y and La 1.85 Sr 0.15 CuO 4 show strong correlations, suggesting that the superconducting state is the same in the two materials. While the overall temperature dependence of R s is reasonably well described by the Bardeen-Cooper-Schrieffer (BCS) theory in the very dirty limit, additional features are seen in R s and also in delta s which suggest detailed deviations from the BCS s-wave state.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{reagor1986inertial,

title = {Inertial dynamics of pinned charge-density-wave condensates. I. NbSe 3},

author = {D Reagor and S Sridhar and G Gruner},

year  = {1986},

date = {1986-01-01},

journal = {Physical Review B},

volume = {34},

number = {4},

pages = {2212},

publisher = {APS},

abstract = {Conductivity measurements are reported for the linear-chain compound 

NbSe

3

 in the frequency range 9–100 GHz. In both charge-density-wave (CDW) states, which develop at 

T

1

=144 K and at 

T

2

=59 K, a strongly frequency-dependent response is observed with Reσ(ω) decreasing with increasing frequency. The behavior is described in terms of a harmonic oscillator response, and in the measured spectral range the expression Re

σ

CDW

(ω)=(

ne

2

τ/

m

*

)[1 /(1+

ω

2

τ

2

)] provides an excellent account of our findings. We evaluate the effective mass 

m

*

 and damping constant τ from a fit to the above equation. The measured effective mass is only weakly temperature dependent, and in both CDW states is in good qualitative agreement with those determined using the theory of Lee, Rice, and Anderson. We also discuss the temperature-dependent damping constant, and a comparison with data taken in the radio-frequency range is given.



Received 28 October 1985

DOI:https://doi.org/10.1103/PhysRevB.34.2212



©1986 American Physical Society},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1986inertial,

title = {Inertial dynamics of pinned charge-density-wave condensates. II. Orthorhombic TaS 3},

author = {S Sridhar and D Reagor and G Gruner},

year  = {1986},

date = {1986-01-01},

journal = {Physical Review B},

volume = {34},

number = {4},

pages = {2223},

publisher = {APS},

abstract = {Complex conductivity 

σ

CDW

(

ω

,T) measurements in the ranges 10–110 GHz and 20–300 K are reported on the charge-density-wave (CDW) material orthorhombic 

TaS

3

. In the CDW state between approximately 130 and 210 K, the complex conductivity obeys a Drude behavior 

σ

CDW

(ω)=(

ne

2

τ/

m

*

)(1+i ωτ), which we associate with damped inertial response of the CDW. The measurements, together with earlier results in the radio-frequency spectral range, enable us to extract all the phenomenological parameters: damping constant τ, effective mass 

m

*

, pinning frequency 

ω

0

, and maximum CDW conductivity 

σ

max

. The experimental results for these parameters are compared with available microscopic theories. The full dynamic response of the CDW between 

10

7

 and 

10

11

 Hz is also presented and shows the conductivity resonance well below the single-particle gap, representing both the relaxational and inertial dynamic response of the collective CDW mode. A comparison is made to similar results on the related CDW compound 

NbSe

3

.



Received 28 October 1985

DOI:https://doi.org/10.1103/PhysRevB.34.2223



©1986 American Physical Society},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1986nonequilibrium,

title = {Nonequilibrium dynamics of quasiparticles in superconductors},

author = {S Sridhar and JE Mercereau},

year  = {1986},

date = {1986-01-01},

journal = {Physical Review B},

volume = {34},

number = {1},

pages = {203},

publisher = {APS},

abstract = {Small changes δ

R

s

 in the 10-GHz surface resistance 

R

s

 of thin superconducting films of Sn and In, caused by an induced static current 

J

0

 have been measured. δ

R

s

 was quadratic in 

J

0

 and both increases (δ

R

s

>0) and decreases (δ

R

s

<0) of absorption were observed. The increase is associated mainly with thermodynamic depression of the gap parameter due to the static current. On the other hand, the decrease of absorption, which implies an enhancement of superconductivity, is incompatible with thermodynamic analysis. A nonequilibrium analysis is presented, according to which the combined static and high-frequency currents cause a nonthermal, time-dependent oscillation of the quasiparticle distribution, and which is out of phase with the driving high-frequency field. The counter oscillation leads to an enhancement of high-frequency supercurrent and decrease of dissipative normal current, and hence results in a decrease of absorption. The analysis describes the experimental results for very thin films of Sn both qualitatively and quantitatively, and with no adjustable parameters. These results lead to the conclusion that at high frequencies, the superconductor responds to time-dependent perturbations in an inherently nonadiabatic, nonequilibrium manner even for vanishingly small high-frequency fields. The implications for several unexplained experiments on the magnetic field dependence of 

R

s

 are discussed.



Received 24 January 1986

DOI:https://doi.org/10.1103/PhysRevB.34.203



©1986 American Physical Society},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1985inertial,

title = {Inertial Dynamics of Charge-Density Waves in Ta S 3 and Nb Se 3},

author = {S Sridhar and D Reagor and G Gruner},

year  = {1985},

date = {1985-01-01},

journal = {Physical review letters},

volume = {55},

number = {11},

pages = {1196},

publisher = {APS},

abstract = {Frequency-dependent complex-conductivity measurements are reported in the charge-density-wave states of Ta S 3 and Nb Se 3, in the 10—100-GHz spectral region. A Drude-type behavior associated with damped inertial response of the condensate is observed for the first time. The fundamental parameters that characterize the dynamics of the collective mode (damping constant, pinning energy, and effective mass) are obtained. The results for the effective mass and damping are compared with microscopic theories.},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{reagor1985inertial,

title = {Inertial charge-density-wave dynamics in (TaSe 4) 2 I},

author = {D Reagor and S Sridhar and M Maki and G Gruner},

year  = {1985},

date = {1985-01-01},

journal = {Physical Review B},

volume = {32},

number = {12},

pages = {8445},

publisher = {APS},

abstract = {Frequency-dependent conductivity measurements are reported in the charge-density-wave (CDW) state of the linear-chain compound (TaSe 4) 2 I in the spectral range 4.5–94 GHz. In contrast to other CDW systems which are overdamped, the response is underdamped, with a resonant frequency of approximately 35 GHz, a resonance width of approximately 20 GHz, and an effective mass of 10 4. The large effective mass, large resonant frequency, and small damping are a consequence of the strong electron-phonon coupling in this system.},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{javadi1985giant,

title = {Giant conductivity resonance in the spin-density-wave state of an organic conductor},

author = {HHS Javadi and S Sridhar and G Grüner and Long Chiang and F Wudl},

year  = {1985},

date = {1985-01-01},

journal = {Physical review letters},

volume = {55},

number = {11},

pages = {1216},

publisher = {APS},

abstract = {Frequency-dependent conductivity measurements between 4.5 and 35 GHz are reported in the spin-density-wave (SDW) state of the linear-chain organic conductor (TMTSF) 2 P F 6, where TMTSF denotes tetramethyltetraselenafulvalenium. A giant conductivity resonance, implying long relaxation times, is observed at frequencies well below the single-particle gap. The frequency dependence is strongly depressed by small amounts of impurities. Either collective spin-density-wave conduction or excitations of the spin-density-wave mode are responsible for the observed frequency-dependent response.},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1985complex,

title = {Complex conductivity measurements between 26 and 110 GHz using complex impedance bridges},

author = {S Sridhar and D Reagor and G Gruner},

year  = {1985},

date = {1985-01-01},

journal = {Review of scientific instruments},

volume = {56},

number = {10},

pages = {1946--1952},

publisher = {American Institute of Physics},

abstract = {A method is described of measuring complex conductivity based upon the measurement of the impedance of a sample placed in a waveguide using a complex impedance bridge. From the observed changes in the bridge parameters, viz., attenuation and phase shift, the impedance and, hence, the complex conductivity are inferred. The principles and details of operation of three bridges covering the frequency range 26 to 110 GHz are discussed. The measurement technique was verified for lossless samples and for lossy resistive wires. An example of temperature and frequency dependent complex conductivity measurements on a linear chain material is presented.},

keywords = {Collective Excitations},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1984microwave,

title = {Microwave dynamics of quasiparticles and critical fields in superconducting films.},

author = {Srinivas Sridhar},

year  = {1984},

date = {1984-01-01},

abstract = {The microwave response of the superconducting state in equilibrium and non-equilibrium configurations was examined experimentally and analytically. Thin film superconductors were mostly studied in order to explore spatial effects. The response parameter measured was the surface impedance.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1983microwave,

title = {Microwave dynamics of quasiparticles and critical fields in superconducting films[Ph. D. Thesis]},

author = {S SRIDHAR},

year  = {1983},

date = {1983-01-01},

abstract = {The microwave response of the superconducting state in equilibrium and non-equilibrium configurations was examined experimentally and analytically. Thin film superconductors were mostly studied in order to explore spatial effects. The response parameter measured was the surface impedance. For small microwave intensity the surface impedance at 10 GHz was measured for a variety of samples (mostly Sn) over a wide range of sample thickness and temperature. A detailed analysis based on the BCS theory was developed for calculating the surface impedance for general thickness and other experimental parameters. Experiment and theory agreed with each other to within the experimental accuracy. Thus it was established that the samples, thin films as well as bulk, were well characterized at low microwave powers (near equilibrium).},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridhar1980effects,

title = {Effects of quasiparticle redistribution on the surface impedance of superconductors},

author = {S Sridhar and JE Mercereau},

year  = {1980},

date = {1980-01-01},

journal = {Physics Letters A},

volume = {75},

number = {5},

pages = {392--394},

publisher = {Elsevier},

abstract = {Calculations of surface impedance of a thin film superconductor indicate a significant decrease, with increasing microwave power, due to quasiparticle redistribution. An expression for the microwave-to-film coupling is derived. The distribution function is solved self-consistently to avoid a singularity.},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{nageshamagnetic,

title = {Magnetic nanoparticle vectors: A tool for diagnosis and therapy},

author = {D Nagesha and R Sawant and P Parimi and E Gultepe and R Bindra and V Torchilin and S Sridhar},

abstract = {Magnetic nanoparticles (NPs) in the form of iron oxide have been extensively used in nanomedicine for targeted drug delivery, magnetic cell sorting and as a contrast agent for magnetic resonance imaging. We have developed a variety of platforms incorporating magnetic nanoparticles for use in diagnosis and therapy. Iron oxide NPs were encapsulated within micelles, liposomes and polymers to form an enclosed system. In an another system, the surfaces of iron oxide NPs were suitably modified to coat with a thin layer of gold to form an iron oxide-gold core-shell NPs structure. Various biomolecules such as antibodies, fluorescent tags, drugs, plasmid DNA and radioactive labels can be attached to the surface of these magnetic nanoparticles through suitable surface chemistry. Cytotoxicity, cell targeting, cellular uptake and T2 relaxation time were studied for use of these various magnetic NPs-based vectors for …},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{sawantpolymeric,

title = {Polymeric Magnetomicelles As a Probe for MRI Imaging: Characterization and Mri Properties},

author = {RM Sawant and D Nagesha and S Sridhar and VP Torchilin},

abstract = {Superparamagnetic iron oxide nanoparticles (SPIONs) coated with silane were prepared and entrapped in polymeric micelles made from PEG-PE using hepes-buffered saline pH 7.4. The SPIONs entrapped in these micelles had excellent stability and did tend to aggregate at the conditions store. In contrast “plain” SPIONs collapsed from solution and did not show any ability to remain dispersed. SPION-micelles thus prepared have shown an improved relaxivity at low concentration of entrapped SPIONs, which makes them to be promising contrast agents for T2 MRI imaging.},

keywords = {MRI},

pubstate = {published},

tppubtype = {article}

}

@article{selvarasahdesign,

title = {Design and implementation of silicon-based optical nanostructures for integrated photonic circuit applications using Deep Reactive Ion Etching (DRIE) technique},

author = {S Selvarasah and R Banyal and BDF Casse and WT Lu and S Sridhar and MR Dokmeci},

abstract = {In this paper, we present the fabrication of nano optical elements by means of deep reactive ion etching technique (Bosch process) on a silicon-on-insulator substrate. The nano structures are fabricated in a two step process. The first step consists of direct-writing nanoscale patterns on PMMA polymer by electron beam lithography. These nano patterns are then transferred to the silicon surface by a low temperature and low pressure deep reactive ion etching (DRIE) process using PMMA as a mask. The low temperature and low pressure conditions in the DRIE process minimize scalloping in the nanoscale features. We found that the etch rate is highly dependent on the aspect ratio of the structure. We have used the DRIE method to fabricate a negative-index photonic crystal flat lens and demonstrated the focusing properties of this flat lens using a near-field scanning optical microscope.},

keywords = {Sensors},

pubstate = {published},

tppubtype = {article}

}

@article{coralnegative,

title = {Negative Refraction in Gold-Dielectric Nanocomposite Arrays},

author = {C Coral-Gomez and S Sridhar and A Friedman and L Menon},

abstract = {It is well known from electrodynamics that the refractive index n of materials is given by the relationship:, where ε> 0 and µ> 0 are the dielectric constant and magnetic permeability of the material where the electro-magnetic waves propagate. In 1968, Russian Physicist Victor Veselago discovered that if the refractive index of materials was negative then a lot of “exotic” physical phenomena might be observed. For instance, of particular interest was the idea of the “flat superlens” that transforms a 3D point object into a 3D image without distortion. Such a superlens could be implemented by means of a flat lens with negative refraction index [1].

At the time that Veselago’s article was published, no material with negative refraction index was known. It was not until 2000, when John Pendry of Imperial College in London suggested that a material with negative refraction index can be created, and that resolutions of the order of …},

keywords = {Nanomaterials},

pubstate = {published},

tppubtype = {article}

}

@article{jacobsplane,

title = {In-Plane and ˆc-Axis Microwave Penetration Depth of Bi2Sr2Ca1Cu2O81d Crystals},

author = {T Jacobs and S Sridhar and Qiang Li and GD Gu and N Koshizuka},

abstract = {The complete temperature dependences of the in-plane and ˆc-axis microwave (10 GHz) penetration depth l (T) and the surface resistance Rs (T) of high quality Bi2Sr2Ca1Cu2O81d crystals are reported. In contrast to earlier measurements, a leading lab~ T dependence is observed at low temperatures, consistent with nodes in the in-plane gap. The overall behavior of lab (T) and Rs ab (T) is similar to that of YBa2Cu3Oy at low T, but differs at temperatures near Tc. The ˆc-axis penetration depth lc (T) is shown to best agree with a model of weakly coupled superconducting layers with nodes in the gap.

},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sridharnegative,

title = {Negative Refraction and Imaging in Photonic Crystals},

author = {S Sridhar and PV Parimi and WT Lu and P Vodo and John S Derov and AFRL Hanscom and MA Bedford},

abstract = {Negative refraction and left-handed electromagnetism in a photonic crystal are demonstrated in waveguide and free space experiments at microwave frequencies. Precision control to achieve tailor-made refractive indices has been achieved. The negative refraction in these photonic crystals is shown to lead to imaging by a flat lens. We have also developed a generalized theory of flat lens imaging. These results promise potential applications in a variety of optical and microwave systems for communications and imaging.},

keywords = {Quantum Chaos},

pubstate = {published},

tppubtype = {article}

}

@article{baldwinnanoformulations,

title = {Nanoformulations of PARP Inhibitors for Cancer Therapy},

author = {Paige Baldwin and Shifalika Tangutoori and Srinivas Sridhar},

abstract = {PARP inhibitors (Poly (ADP-ribose) polymerase inhibitors) such as Olaparib are among the most potent molecular inhibitors used in clinical trials for various types of cancers including prostate and ovarian cancers They act by inhibiting DNA damage repair and thus accumulating deleterious mutations leading to genetic instability as a function of number of cell replications. Thus, in this study, we thoroughly characterized and optimized the in vitro model of prostate cancer (PC3, LNCaP, FK01) and ovarian cancer (PA1), in a 96 well system. To compare and contrast the IC-50’s, of free drug and nanoformulated drug, we employed dose response curves generated for each cell line. Prior to this, it was crucial to develop growth rate curves for all cell lines and optimize the seeding density so as to ensure that cell death was not occurring because of over confluence and lack of nutrients, but rather due to the genetic instability caused by the treatment. These curves allow for each cell line to be exposed to the treatment of choice for 4 doubling cycles prior to analysis. Dose response was generated for 4 cell lines, with the 2 different drugs (Olaparib and nano-Olaparib). We determined the IC-50’S of these cells after 4 doubling cycles. These results allowed for comparison between the efficacy of the nanoformulation versus the free drug, thus determining the dose regimen for further invitro studies},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{barlowmicroencapsulation,

title = {Microencapsulation of Bacteria for Controlled Release of Bioactives},

author = {Jacob Barlow and Kevin Gozzi and Chase Kelley and Anne Van De Ven-Moloney and Yunrong Chai and Srinivas Sridhar},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{baldwinparp,

title = {PARP Inhibitor Nanotherapy for Cancer Treatment},

author = {Paige Baldwin and Anders Ohman and Anne van de Ven and Daniela Dinulescu and Srinivas Sridhar},

abstract = {Poly (ADP-ribose) Polymerase (PARP) plays an important role in a number of DNA repair pathways. PARP inhibitors, such as Olaparib exploit the concept of synthetic lethality by selectively targeting cancer cells with defective DNA repair pathways, while leaving healthy cells with multiple repair pathways unharmed. These drugs are currently only available in oral form which results in limited bioavailability, poor tumor accumulation, and systemic toxicity. Nanoparticle formulations of Olaparib were developed to allow intravenous (IV) or intraperitoneal (IP) delivery, providing greater bioavailability and tumor accumulation, while limiting systemic toxicities. NanoOlaparib was synthesized and characterized before further testing in vitro and in vivo. In vitro it has been tested in a panel of ovarian cancer cell lines to elucidate sensitivity profiles. NanoOlaparib was also tested in an ovarian cancer IP spread model. Animals were treated IP with NanoOlaparib alone, and in combination with cisplatin. Bioluminescence imaging illustrated that NanoOlaparib administered IP daily resulted in a greater inhibition of tumor growth than those treated with oral Olaparib daily. Radiosensitization with NanoOlaparib was tested in a radiation resistant prostate cancer cell line, FK01 and a xenograft model with the same cells to mimic castration resistant prostate cancer. The FK01 xenografts are highly radioresistant with little difference between untreated and radiation only animals. NanoOlaparib delays tumor growth, while the combination of radiation and NanoOlaparib shrinks tumors. These results show that NanoOlaparib amplifies the therapeutic efficacy of PARP …},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{weiproperties,

title = {PROPERTIES OF SUPERCOOLED LiCl RH O SOLUTIONS},

author = {YAN-ZHEN WEI and S SRIDHAR},

abstract = {The relation between the dynamics of dielectric relaxation, the glass-forming ability and properties in the supercooled state of LiCl: RH, O solutions are investigated, via measurements of the dielectric spectra between 45 MHz and 20 GHz and temperatures between 210 K and 300 K and concentrations R< 20. For high concentration glass-forming solutions, a close correspondence between the temperature dependencies of the Cole-Cole relaxation time t, the conductivity, and the viscosity, is observed.,(T) is well-described by a power law form (TT,)', with T.,-205 K and y-2, a form motivated by mode-coupling theory. The data suggest that non-Debye response at room temperature is associated with the ability to vitrify at low temperatures. A microscopic basis for the avoidance of crystallization is provided by obtaining from the dielectric data the mean radius available to a water molecule, which is shown to approach 19 …},

keywords = {Chemical & Biological Physics},

pubstate = {published},

tppubtype = {article}

}

@article{kumarsupporting,

title = {Supporting information Nanoparticles based brachytherapy spacers for delivery of localized combined chemo-radiation therapy},

author = {Rajiv Kumar and Jodi Belz and Stacey Markovic and Tej Jhadav and William Fowle and Mark Niedre and Robert Cormack and Mike G Makrigiorgos and Srinivas Sridhar},

abstract = {Synthesis of NIR fluorescent Silica nanoparticles: The synthesis of conCy7. 5-SNPs was carried out using oil-inwater microemulsion method, following a previously reported protocol with several modifications.(1-2) For conjugating the Cy7. 5 fluorophore in the SNPs, Cy7. 5-NHS ester was first conjugated to a silane precursor using aminopropyltriethoxy silane. 5 mg Cy 7.5 NHS ester (6.4 μmol), 1.77 mg APTES (8 μmol) and 10 μl neat triethylamine were added to 1 ml of anhydrous DMSO and stirred over night at room temperature under Ar atmosphere. The crude mixture was purified using EtOAc-hexane mixture, dried and resuspended in 1ml of DMSO. For synthesizing the Cy7. 5 conjugated ORMOSIL nanoparticles, 10ml of 2.2%(w/v) surfactant AOT solution was prepared in HPLC grade water followed by addition of 600 μl of n-butanol and 50 μl of Cy7. 5-silane under vigorous stirring at rt After 15 min of stirring 100ul of neat VTES was added and resultant reaction mixture was stirred for another 45 minutes. Finally 10ul of NH4OH was added and reaction was allowed to stir overnight. The nanoparticles suspension was then dialyzed against distilled water for 48h at room temperature, using a cellulose membrane with a cut-off size of 12-14 kDa. Following dialysis, the nanoparticles were sterile filtered and stored at 4 C for future use.

Fabrication of INCeRT spacers: For fabricating the spacers, the extracted SNPs from the aqueous mother liquor required a careful assessment, in terms of solvent compatibility with the PLGA polymer, so that both can be dispersed in a single phase without disturbing the integrity of the nanoparticles and the …},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{srikanthevidence,

title = {Evidence for Short-range Magnetic Order and Spin-gap? The broad peaks between 400 cm},

author = {H Srikanth and B Revcolevschi and S Sridhar and L Pinsard and A Revcolevschi},

keywords = {Magnetism},

pubstate = {published},

tppubtype = {article}

}

@article{kennedyli,

title = {li. EQUENCY-UEPENDENCE OF THE MICROWAVE SURFACE RESISTANCE OF CERAMIC У, Вп2Си30 „},

author = {WL Kennedy and C Zahopoulos and S Sridhar},

abstract = {The frequency dependence оГ the surface resistance Rj of ceramic Y^ BaaGujÓgv; ik measured between 5 GHz and 20 GJlz in both the normal a. nd superconducting states. Tlie measurements were carried out using a, fully superconducting resonant cavity T made of the oxide superconductor. The surface resistance was found to vary as R, к f, with 7= 0.0±0.2 at 118 1С in the normal state, and у= 2.0±0.3 in the superconducting state. The normal stale results are consistent in magnitude and frequency dependence with the classical skin effect, and the quadratic dependence in the superconducting state clearly indicates a local electrodynamics оГ a Josephson-coupled network.

The microwave response of the recently discovered oxide superconductors is of considerable interest, both from a fundamental scientific and technological viewpoint. Several measurements of the temperature dependence of the surface …},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{balincreased,

title = {Increased Nanoparticle Uptake Under Disturbed Flow-Induced Degraded Glycocalyx Conditions},

author = {Nandita Bal and Ming Cheng and Rajiv Kumar and Srinivas Sridhar and Eno Ebong},

abstract = {Results: The partial LCA ligation model achieved the goal of creating a vessel with disturbed flow and provided a convenient comparison with a healthy RCA experiencing streamlined flow. The vessel walls of the LCA also exhibited a more discontinuous GCX layer on the intima as compared to the RCA, decreasing from 76.3±10.2% in the RCA to 21.2±5.9% in the LCA. This observable dysfunction correlated to increased nanoparticle uptake, as the LCA took in approximately 2.5-fold more GNS than the RCA did, based on the fluorescence signal detected in the histology images. This was imaged at 10 times magnification (Fig 1) and 63 times magnification (Fig 2).

Conclusions: A partial LCA ligation was performed to acutely disturb blood flow in a mouse vessel and observe resultant endothelial GCX dysfunction as well as passive targeting of GNS to affected areas. The affected LCA exhibited lack of continuous GCX layer, as well as increased localization of PEG coated GNS that are designed to deliver drug therapies. These results indicate that vessel and GCX dysfunction, both precursors of atherosclerosis and cardiovascular disease, can be induced in a mouse model to study targeted drug delivery. Passive nanoparticle uptake differences between the healthy RCA and disturbed LCA indicate a role of GCX infiltration of nanoparticles to the endothelial cells. Targeting dysfunctional vessels based on the GCX offers a new approach in cardiovascular disease therapy and prevention.},

keywords = {Nanomedicine},

pubstate = {published},

tppubtype = {article}

}

@article{gharagouzloofunctional,

title = {Functional neuroimaging using dynamic radial 3D UTE pulse sequences},

author = {Codi Amir Gharagouzloo and Chao Ma and Eline E Verwer and Joseph B Mandeville and Chuan Huang and Srinivas Sridhar and Georges El Fakhri and Dustin W Wooten and Marc D Normandin},

abstract = {Functional MR neuroimaging is an essential tool for studying brain activity. Cerebral blood volume (CBV) is an important indicator of brain function, but measurements are typically qualitative or relative. Furthermore, warping and signal drift necessitate significant image pre-processing with standard EPI acquisition. In this work, we utilize a radial 3D UTE pulse sequence with optimized acquisition parameters determined from phantoms and modeling. Feasibility of dynamic UTE as a functional neuroimaging method is demonstrated in non-human primates receiving NBOH-2C-CN, a 5-HT2A receptor agonist. CBV is measured dynamically throughout the whole brain and shown to agree well with an analogous EPI experiment.



PURPOSE

The three primary physiological indicators of neural activity in fMRI are changes in cerebral blood volume (CBV), blood flow and oxygenated state of hemoglobin.To isolate the CBV-induced signal change, T2*-weighted echo-planar imaging (EPI) sequences are commonly utilized with intravascular contrast agent to overshadow contrast from changes in blood oxygenation and enhance signal from CBV changes. While EPI sequences are fast, they are prone to significant distortion artifact. Additionally, macroscopic susceptibility artifacts confound the MR signal and are difficult to separate from baseline blood oxygenation level dependent (BOLD) effects; thus results are qualitative. Ultra-short time-to-echo (UTE) sequences are insensitive to susceptibility changes and extravoxular signal dephasing. Thus, we propose to use quantitative UTE contrast-enhanced (QUTE-CE) MRI to measure CBV changes dynamically.



METHODS

QUTE-CE MRI is the combination of acquisition with an optimized 3D UTE pulse sequence and an intra-vascular contrast agent1 to render a highly quantitative signal. Ferumoxytol (Feraheme, AMAG Pharmaceuticals, Waltham, Massachusetts, USA) was used for contrast.



Relaxation rates were measured in 1% heparinized whole-calf-blood (Fig. 1a,-c) and modeling with the spoiled gradient echo (SPGR) equation was used to determine optimized parameters for efficient dynamic scans (Fig. 1d). CBV is calculated by simple partial volume calculations. The effect of signal modification by vascular water molecule exchange is suppressed with low TR and high FA2. Modeling signal intensity with two compartments:



IM=fBIb+(1−fB)IT



where, IT is the brain tissue intensity, IB is the blood intensity and fB is the fraction of the voxel occupied by blood. For each image volume, CBV is calculated voxel-by-voxel by subtracting a pre-contrast image then scaling the results by the blood intensity as determined in a large vessel:



fB=CBV=I,M−IMI,B−IB



Animal experiments were conducted under an approved IACUC protocol. A dynamic QUTE-CE study was performed with ferumoxytol on a non-human primate (NHP) with NBOH-2C-CN, a potent and selective 5-HT2A receptor agonist, and results were compared to the current gold standard EPI + ferumoxytol imaging. All imaging was performed on a Siemens 3T Tim Trio magnet. NHPs were anesthetized throughout the scan with isoflurane (1-3%). EPI and UTE scans consisted of three imaging phases: pre-contrast followed by a bolus of 10mg/kg ferumoxytol post-contrast and then administration of 50 mcg/kg of NBOH-2C-CN. Single-shot EPI was accelerated in the phase-encode direction by a factor of two providing an isotropic spatial resolution of 1.3mm and TE=23ms.



RESULTS

QUTE-CE pre-contrast images rendered dark blood with a small amount of tissue contrast in NHPs (Fig. 2a). Bright positive contrast of the blood was achieved after injection of ferumoxytol (Fig. 2b-d). Vasculature was clearly visible and all parts of the anatomy were free of image warping (Fig 2a-c). In contrast, time-averaged EPI data equal to the duration of the dynamic UTE scan exhibited significant signal dropout in the anterior and posterior brain, with obvious image warping (Fig 2f). The same custom-built 8-channel receive coil was used in both acquisitions. Maps of absolute CBV obtained from pre- and post-contrast UTE images are of high quality and have quantitative values consistent with expectation (Fig. 2e).



A dynamic QUTE-CE scan was performed with 1m57s time-resolution. Total scan duration was ~1.5 hours, including 48min prior to NBOH-2C-CN challenge and ~52min of data featuring drug-induced CBV changes. NBOH-2C-CN primarily affect the cortex where 5-HT2A receptors exist in high density. CBV measurements from the full cortex were compared to a separate identical experiment with EPI acquisition. Absolute CBV was measured in the cortex using the dynamic UTE method (Fig. 3b). Relative CBV changes measured by EPI and UTE exhibit strong correlation of temporal features of the response and reasonable agreement in magnitude (Fig 3c).



DISCUSSION

Sparse radial sampling is being investigated to accelerate acquisition time for each UTE volume, thereby improving the dynamic frame rate. The apparent disadvantage of a T1-based method given the high r2/r1 ratio of ferumoxytol might well be mitigated in the context of slow frequency changes, such as when study pharmacological responses3. Similar effects are presumed to occur for ASL in relation to BOLD signal4. In analogy to ASL, which has smaller signal changes than BOLD, smaller absolute signal changes in T1-based methods might find application at low frequencies due to the absolute normalization, which could remove much of the drift.

CONCLUSION

To conclude, we achieved time-resolved functional imaging of brain vasculature in NHPs with a radial 3D UTE pulse sequence. Images do not exhibit spatial warping seen in EPI data and yields quantitative CBV measurements devoid of time-varying signal drift. Without baseline correction, the technique produces relative results that agree well with those obtained in a separate EPI experiment.

Acknowledgements

This work was supported in part by funding from NIH R01MH100350 (MDN) and by NIH T32EB013180 (GEF).

References

1. Gharagouzloo, C. A., Mcmahon, P. N. & Sridhar, S. Quantitative contrast-enhanced MRI with superparamagnetic nanoparticles using ultrashort time-to-echo pulse sequences. Magnetic Resonance in Medicine (2014). doi:10.1002/mrm.25426.



2. Kim, Y. R., Rebro, K. J. & Schmainda, K. M. Water exchange and inflow affect the accuracy of T1-GRE blood volume measurements: Implications for the evaluation of tumor angiogenesis. Magn. Reson. Med. 47, 1110–1120 (2002).



3. Jenkins, B. G. Pharmacologic magnetic resonance imaging (phMRI): Imaging drug action in the brain. NeuroImage 62, 1072–1085 (2012).



4. Wang, J. et al. Arterial spin labeling perfusion fMRI with very low task frequency. Magn. Reson. Med. 49, 796–802 (2003).},

keywords = {MRI},

pubstate = {published},

tppubtype = {article}

}

@article{srikanthhigh,

title = {HIGH FREQUENCY MAGNETO-ELECTRODYNAMICS OF Lal. xSrxMnO 3 SINGLE},

author = {H Srikanth and B Revcolevschi and S Sridhar and L Pinsard and A Revcolevschi},

abstract = {The radio frequency (RF) response of La1-xSrxMnO3 single crystals reveal a variety of features associated with the structural, electronic and magnetic properties of the system. The resonance technique operating at ∼ 4 MHz employed in this study is sensitive to small changes in both the magnetic susceptibility and resistivity of the samples. Very sharp changes in frequency are observed at the ferromagnetic (FM) and structural phase transitions in both the metallic (x = 0.175) and insulating (0.125) crystals studied.



In addition to the known transitions identified as FM and orthorhombic distortions, our experiments show rich structures which are not observed in conventional DC magnetization and transport experiments. Our results demonstrate that RF experiments are ideally suited to investigate the complex phase diagram in the manganites.



The colossal frequency change that we observe at the FM transition in the La1-xSrxMnO3 crystals is indicative of the enormous potential for using these materials in high frequency switching applications.},

keywords = {Magnetism},

pubstate = {published},

tppubtype = {article}

}

@article{kuskopublication,

title = {Publication: Journal of Superconductivity Pub Date: 2001},

author = {C Kusko and Z Zhai and RS Markiewicz and S Sridhar},

keywords = {Superconductivity},

pubstate = {published},

tppubtype = {article}

}

@article{sawantdeveloping,

title = {Developing superparamagnetic iron oxide nanoparticles as tumor-specific magnetic resonance imaging (MRI) contrast agents},

author = {RM Sawant and E Gultepe and D Nagesha and S Sridhar and VP Torchilin},

abstract = {Superparamagnetic iron oxide nanoparticles (SPION) have received increased interest due to their characteristic small size ca 4-10 nm and excellent T2-type MRI contrast properties. However, uncoated-“plain” SPION have a tendency to aggregate and thus are not stable at normal physiological conditions. In this work we load the SPION in polymeric polyethylene glycol phosphatidyl ethanolamine (PEG-PE) micelles and additionally surface-modify with anticancer anti-nucleosome antibody 2C5.(mAb 2C5). SPION-loaded PEG-PE micelles were stable with the size ranging from 20 to 40 nm. The conjugation of mAb 2C5 was gentle and there was almost no loss in activity of the antibody after conjugation. SPION-loaded mAb 2C5 immunomicelles were able to recognize and bind with human breast cancer MCF-7 cells in vitro significantly higher when compared to SPION-loaded “plain” micelles or SPION-loaded “non …},

keywords = {MRI},

pubstate = {published},

tppubtype = {article}

}