Search Results - (Author, Cooperation:C. Kumar)

2018-05-30

American Physical Society (APS)

0556-2821

1089-4918

Physics

Strong Interactions

2016-03-05

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

book

2022

Vergleichende Erziehungswissenschaft ; Bildungspolitik ; Internationale Erziehung ; Hochschulbildung ; Hochschulbindung ; Hochschulsystem

English

farbige Illustrationen 7

2018-06-21

Royal Society

2054-5703

Natural Sciences in General

nuclear chemistry, environmental chemistry

2018-04-19

Royal Society

2054-5703

Natural Sciences in General

biomaterials, biomechanics, biomimetics

1089-7550

AIP Digital Archive

Physics

A rapid thermal annealing (RTA) technique has been employed to process lead zirconate titanate (PZT) films prepared by reactive magnetron sputtering. The films were fabricated by dc sputtering a multielement metal target in an oxygen ambient at a substrate temperature of 200 °C. A subsequent postdeposition RTA at 600 °C for 5 s crystallizes the films into a perovskite-type structure through various intermediate phases. Due to the short postdeposition processing times inherent in the RTA method, the initial nature of the as-grown films has a critical influence on the crystallization kinetics. The reaction sequence in the formation of perovskite PZT from the films deposited at low substrate temperatures by the sputtering technique has been evaluated, and various key factors influencing the crystallization of PZT have been identified. As-grown films are constituted of polycrystalline orthorhombic lead oxide in an amorphous matrix of titania and zirconia. During annealing lead oxide transforms into a cubic phase, and the lead oxide stoichiometry determines the processing route to PZT. In the case of lead-rich films, intermediate compounds of lead with titania and zirconia are observed, which react during the final stage of annealing at 600 °C to form PZT. In lead-deficient films, the formation of a pyrochlore phase has been observed, which crystallizes into perovskite at 750 °C. The Zr/Ti ratio also influences the crystallization sequence. In the case of Ti-rich PZT, the intermediate compounds initially involve a zirconium-rich rhombohedral PZT, with which residual titanium reacts to form tetragonal PZT. The films showed good ferroelectric and other electrical properties with a remanent polarization of 24 μC/cm2, coercive field of 32 kV/cm, ε'=950, tan δ=0.02, and σdc (300 K)=10−12 Ω−1 cm−1 with an activation energy between 0.9 and 1.4 eV.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The kinetics of the amorphous-to-tetragonal transformation has been studied in sol-gel-derived thin films of zirconia deposited on alumina substrates. A rapid-thermal-annealing system was used which allowed good control of processing parameters such as temperature and heating rates. The effect of these two parameters on the transformation kinetics was studied and the experimental results were analyzed in terms of conventional nucleation and growth models. The use of two-step thermal processing cycles shows potential for the modification of the microstructural features of crystallized films and for a reduction in processing times.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

This paper reports the design of a compact, inexpensive, and ultrahigh vacuum compatible reed-type Kelvin probe for work function and surface photovoltage spectroscopy (SPS) studies. A simple method of controlling the vibration amplitude of the probe is proposed which reduces mechanical instabilities of the vibrating capacitor, leading to an autonomous and reliable probe for monitoring work function changes over a prolonged period of time. A boss-type reference gold electrode is used to simultaneously study the work function changes with adsorbents and SPS on real surfaces of semiconductors. A current preamplifier used in the measuring circuit reduces the effect of parasitic input capacitance and facilitates the application of a biasing voltage. A feedback loop system and off-null technique are used for obtaining the contact potential difference. With this improved design of the probe setup a sensitivity of better than 0.1 mV has been achieved. Some experimental results are presented to show the performance of the setup. © 1996 American Institute of Physics.

Electronic Resource

1525-1314

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

The Palghat Gap region is located near the centre of the large southern Indian granulite terrane. at the northern edge of the Kodaikanal charnockite massif. The dominant rock types in the region are hornblende-biotite ± orthopyroxene gneisses and charnockites along with minor amounts of intercalated mafic granulite, metapelite and calc-silicate. The P-T estimates from garnetiferous mafic granulites and metapelite samples are generally in the range 9-10 kbar and 800-900d̀ C using both conventional thermobarometric methods and the TWEEQU thermobarometry program. These P-T estimates, which should be taken as minimum values, are among the highest yet reported for South Indian and Sri Lankan granulites. The occurrence of orthopyroxene + plagioclase symplectites around embayed garnet grains in the mafic granulites and cordierite rims around garnet grains in metapelite suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates c. 3 and 7 kbar decompression at high temperature in the mafic granulites and metapelite, respectively. In both rock types, the key to the determination of the retrograde P-T path was the recognition of small amounts of second generation plagioclase with a more anorthitic composition than the matrix plagioclase. The preservation of high garnet-pyroxene temperatures in the mafic granulites (despite small garnet grain size) suggests rapid cooling of the terrane. Calculated minimum cooling rates range from 8 to 80d̀ C Ma-1. Such cooling rates are more rapid than those associated with normal isostatic processes and suggest that the terrane was tectonically exhumed at high temperature.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Stable transfection of the human neuroblastoma cell line SH-SY5Y with the human 5-hydroxytryptamine2A (5-HT2A) or 5-HT2C receptor cDNA produced cell lines demonstrating ligand affinities that correlated closely with those for the corresponding endogenous receptors in human frontal cortex and choroid plexus, respectively. Stimulation of the recombinant receptors by 5-HT induced phosphoinositide hydrolysis with higher potency but lower efficacy at the 5-HT2C receptor (pEC50 = 7.80 ± 0.06) compared with the 5-HT2A receptor (pEC50 = 7.30 ± 0.08). Activation of the 5-HT2A receptor caused a transient fourfold increase in intracellular Ca2+ concentration. Whole-cell recordings of cells clamped at −50 mV demonstrated a small inward current (2 pA) in response to 10 µM 5-HT for both receptors. There were no differences in potency or efficacy of phosphoinositide hydrolysis among four hallucinogenic [d-lysergic acid diethylamide (LSD), 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI), 5-methoxy-N,N-dimethyltryptamine, and mescaline] and three nonhallucinogenic drugs (m-chlorophenylpiperazine, quipazine, and ergotamine). Comparison of equipotent doses producing 20% of the maximal response induced by 5-HT revealed selective activation of the 5-HT2A receptor by LSD and to a lesser degree by DOI, mescaline, and ergotamine. Quipazine and 5-methoxy-N,N-dimethyltryptamine were relatively nonselective, whereas m-chlorophenylpiperazine selectively activated the 5-HT2C receptor. It is unlikely therefore that hallucinosis is mediated primarily by activity at the 5-HT2C receptor, whereas activity at the 5-HT2A receptor may represent an important but not unique mechanism associated with hallucinogenic drug action.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Lead zirconate titanate films have been fabricated by a dc sputtering technique with a post deposition rapid thermal annealing treatment at 650 °C for 10 s. The films exhibited good structural, dielectric, and ferroelectric properties compared to conventional furnace-annealed films. The measured dielectric constant and loss tangent at 1 kHz were 900 and 0.04 and the remanent polarization and coercive field values were 10 μC/cm2 and 23 kV/cm, respectively. No significant fatigue in polarization was observed in the films up to 1010 cycles of bipolar stress. The films were optically transparent and showed a linear electro-optic (EO) effect after poling with an EO coefficient of 1.5×10 −11 m/V.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Indium tin oxide films have been deposited by rf sputtering an oxide target (90% In2O3+10% SnO2). Transparent conducting films have been obtained on room-temperature substrates without any post-deposition annealing. The effects of target-substrate separation on the growth characteristics and film properties have been studied. The virtual-source formation of the sputtered neutrals in the gap between the target and substrate has been observed. The effect of sputtering parameters on the position of the virtual source has been studied. It has been observed that the films deposited onto substrates kept below and above the virtual source have different properties. The films on substrates kept above the virtual source have (222) preferred orientations, with a direct optical band gap of 3.7 eV, an electron effective mass of 0.51 m, and a figure of merit ∼14×10−3 Ω−1. The films on substrates below the virtual source have preferred orientations along (440) and (400), with a band gap of 3.5 eV, an effective mass of 0.2 m, and a higher figure of merit ∼40×10−3 Ω−1.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The fabrication of new ferroelectric modified lead iron niobate films having an approximate composition Pb[(Fe0.7Cr0.2Ni0.1)0.5Nb0.5]O3 is reported. A magnetron sputtering technique was used for the deposition of the films and a post-deposition annealing at 800 °C for 5 s in a rapid thermal processing furnace crystallizes the films principally into a perovskite-type structure. Ferroelectricity in these films was confirmed by the presence of hysteresis loops, with a remanent polarization of 15 μC/cm2, and coercive field of 100 kV/cm. The room-temperature dielectric constant measured at 1 kHz was 640 and the dissipation factor was 0.1.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The fabrication of hexagonal barium titanate films by sputtering technique is reported. Compressed powders of hexagonal barium titanate were sputtered in argon/oxygen gas mixtures. The as-grown films were amorphous and a post-deposition annealing above 700 °C resulted in the crystallization of the films with hexagonal crystal structure. Transmission electron microscopy was used to study the crystallization of the amorphous films.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Ferroelectric lead niobate (PbNb2O6) exists in an orthorhombic phase at room temperature. The fabrication of lead niobate in this ferroelectric form has often been reported to be difficult due to the stabilization of nonferroelectric phases during processing. In this letter, the stabilization of the orthorhombic phase in magnetron sputtered lead niobate films using "pulsed thermal processing'' is reported, and various processing factors which influence the destabilization of this phase are discussed. The room-temperature dielectric constant and loss tangent of the resulting films at 1 kHz were 320 and 0.4, respectively. Polarization versus electric-field hysteresis loops showed no saturation, with a remanent polarization of 15 μC/cm2 and a coercive field of 500 kV/cm. The films were highly resistive with a dc conductivity of 1−10 Ω−1 cm−1 at 300 K.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

On two separate occasions, a 78-year-old obese man suffering from congestive cardiac failure and peripheral vascular disease, required epidural anaesthesia for surgery to his leg. The dosage requirement on the first occasion was large and much greater than on the second occasion. Reasons for the difference in dosage are discussed. We suggest an epidural catheter should be inserted 3 cm into the epidural space.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Routine pre-operative evaluation of a 58-year-old man scheduled for repair of an inguinal hernia, disclosed a blood pressure of 200/100 mmHg. This decreased to 150/100 mmHg after a period of rest. An electrocardiogram taken as a result of this chance finding showed left bundle branch block. There were no other cardiovascular symptoms or signs. Soon after induction of general anaesthesia, the conduction defect disappeared. The return to sinus rhythm was sudden and sustained and was not related to changes in heart rate or blood pressure. One month later, his electrocardiograph remained normal.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource