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匹配条件: “Rajiv. P” ,找到相关结果约200869条。
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Neutron spectra of Herbertsmithite Materials: Observation of a Valence Bond Liquid phase?
Rajiv R. P. Singh
Physics , 2010,
Abstract: We argue that neutron spectra in a short-range ordered Valence Bond state is dominated by two-spinon states localized in small spatial regions such as a pinwheel. These excitations lead to angle averaged dynamic structure factor that is spread over a wide frequency range up to about $2.5 J$, whereas its wavevector dependence at all frequencies remains very close to that of isolated dimers. These results are in excellent agreement with recent Neutron scattering data in the Herbertsmithite materials ZnCu$_3$(OH)$_6$Cl$_2$.
Spinons, Solitons and Magnons in One-dimensional Heisenberg-Ising Antiferromagnets
Rajiv R. P. Singh
Physics , 1995, DOI: 10.1103/PhysRevB.53.11582
Abstract: We calculate the excitation spectra for the one-$d$ Heisenberg-Ising antiferromagnets by expansions around the Ising limit. For $S=1/2$, the calculated expansion coefficients for the spinon-spectra agree term by term with the solution of Johnson and McCoy. For $S=1$, the solitons become gapless before the Heisenberg limit is reached, signalling a transition to the Haldane phase. By applying a staggered field we calculate the one-magnon spectra for the $S=1$ Heisenberg chain. For $S=3/2$ the quantum renormalization of the spin-wave spectra is calculated to be approximately $1.16$.
Exchange Constants and Neutron Spectra of Iron Pnictide Materials
Rajiv R. P. Singh
Physics , 2009,
Abstract: We show that the neutron scattering spectra observed in CaFe$_2$As$_2$ by Zhao et al (arXiv:0903.2686v1) and the highly unusual spatially anisotropic exchange constants in the iron pnictides derived by Han et al (Phys. Rev. Lett. 102, 107003 (2009)), using electronic structure calculations, can be explained by assuming a role for orbital order in these materials. We write down a simple model Hamiltonian with tertagonal symmetry, whose spin-wave spectra describes the observed dispersion relations. We further argue that these materials have orbital selective Mott transition, which is driven by superexchange between neighboring iron atoms. We suggest that reduced spin and quasi-one dimensionality and not frustration are responsible for the reduced moments in these materials.
Towards goal-directed therapy of hepatorenal syndrome: we have the tools but we need the trials
Rajeshwar P Mookerjee, Rajiv Jalan
Critical Care , 2008, DOI: 10.1186/cc6804
Abstract: Decompensated cirrhosis is characterized by severe circulatory derangements including progressive splanchnic vasodilatation and portal hypertension. These derangements result in several of the complications of advanced cirrhosis, such as increasing ascites and hepatorenal syndrome (HRS). The splanchnic vasodilatation in turn results in relative arterial underfilling [1], with consequent activation of the neurohumoral system, leading to vasoconstriction of numerous vascular beds including the liver, the kidney and the brain [2]. The more advanced the disease, the greater the activation of these neurohumoral factors, most maximal in the state of HRS [3]. Management of tense ascites in the context of evolving HRS has been debated with the concern that a large-volume paracentesis may evoke paracentesis-induced circulatory dysfunction despite volume replacement, thereby further potentiating HRS.The study reported by Umgelter and colleagues in the previous edition of Critical Care describes the single and combined effects on haemodynamics and renal function of plasma expansion with albumin and paracentesis in patients with tense ascites and HRS [4]. Maintenance of the global end-diastolic volume was achieved by invasive monitoring of the central volume. The study's key findings were a demonstration that the cardiac index in HRS patients was fluid responsive despite a normal central venous pressure, and that the reduction in intra-abdominal pressure following paracentesis was associated with an improvement in renal function in the context of fluid substitution guided by assessment of the global end-diastolic volume. In their uncontrolled study, a transpulmonary thermodilution technique (the PiCCO system, Pulsion Medical Systems, AG) facilitated measurement of both cardiac output as well as intrathoracic and pulmonary blood volumes. A subtraction of the pulmonary blood volume from the intrathoracic blood volume enabled an estimate of the 'central' blood volume, referred to
Renal sparing surgery for perirenal liposarcoma: 24 months recurrence free follow up
Gupta, Narmada P.;Yadav, Rajiv;
International braz j urol , 2007, DOI: 10.1590/S1677-55382007000200009
Abstract: liposarcoma is the most common pathology seen in the soft tissue sarcoma of retroperitoneum. these tumors have been traditionally treated with radical surgery sacrificing adjacent organs to achieve clear margins. we have reported our experience of renal sparing surgery for perirenal liposarcoma in two patients with more than 24 month disease free survival.
Eggshell calcification of kidney in ureteropelvic junction obstruction
Gupta, Narmada P.;Yadav, Rajiv;
International braz j urol , 2006, DOI: 10.1590/S1677-55382006000500008
Abstract: eggshell calcification of kidney in case of ureteropelvic junction obstruction (upjo) is an uncommon finding with only a few cases reported in literature. we report a thirty-year-old symptomatic man with curvilinear calcification in hydronephrotic right kidney. thorough investigations to rule out genitourinary tuberculosis and hydatid disease of kidney were performed prior to the definitive management by laparoscopic approach.
Effect of Sm Substitution on Structural, Dielectric, and Transport Properties of PZT Ceramics
Rajiv Ranjan,Rajiv Kumar,R. N. P. Choudhary
Physics Research International , 2009, DOI: 10.1155/2009/382578
Abstract: The polycrystalline samples of Pb1?Sm(Zr0.45Ti0.55)1?/4O3 (PSZT) (where   =  0.00,  0.03,  0.06, and 0.09) were prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the materials at room temperature has confirmed their formation in single-phase with tetragonal crystal structure. The temperature dependence of dielectric response of the samples at selected frequencies has exhibited their phase transition well above the room temperature. The variation of ac conductivity with temperature and the value of activation energy reveal that their conduction process is of mixed type (i.e., singly ionized in ferroelectric region and doubly ionized in paraelectric phase).
Chromatin from Peripheral Blood Mononuclear Cells as Biomarkers for Epigenetic Abnormalities in Schizophrenia
David P. Gavin,Rajiv P. Sharma
Cardiovascular Psychiatry and Neurology , 2009, DOI: 10.1155/2009/409562
Abstract: Background. Studies have implicated abnormalities in epigenetic gene regulation in schizophrenia. Presentation. We hypothesize that identifying abnormalities in chromatin structure and the epigenetic machinery in peripheral blood mononuclear cells (PBMC) from schizophrenia patients could (a) help characterize a subset of schizophrenia patients and (b) lead to targeted pharmacological interventions. Testing. Investigate the relationship between clinical symptoms, demographics, hormonal fluctuations, substance abuse, disease characteristics across the major mental illnesses, and epigenetic parameters in PBMC. In addition, examine the effects of individual antipsychotics, mood stabilizers, as well as experimental agents both as clinically prescribed as well as in cultured PBMC to understand the effects of these agents on chromatin. Implications. If PBMC could serve as a reliable model of overall epigenetic mechanisms then this could lead to a “biomarker” approach to revealing pathological chromatin state in schizophrenia. This approach may provide an informed method for selecting chromatin modifying agents for psychiatric disorders.
Spin-wave excitation spectra and spectral weights in square lattice antiferromagnets
Rajiv R. P. Singh,Martin P. Gelfand
Physics , 1995, DOI: 10.1103/PhysRevB.52.R15695
Abstract: Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin-wave spectra for square lattice, $S=1/2$ Heisenberg-Ising antiferromagnets. The calculated spin-wave spectrum for the Heisenberg model is close to but noticeably different from a uniformly renormalized classical (large-$S$) spectrum with the renormalization for the spin-wave velocity of approximately $1.18$. The relative weights of the single-magnon and multi-magnon contributions to neutron scattering spectra are obtained for wavevectors throughout the Brillouin zone.
Tests of magnetic Hamiltonians for CaV_4O_9
Martin P. Gelfand,Rajiv R. P. Singh
Physics , 1997,
Abstract: We study the uniform magnetic susceptibility and spin-gap for recently proposed Heisenberg model Hamiltonians for CaV_4O_9 based on the orbital ordering scenario of Marini and Khomskii and the LDA calculations of Pickett. We argue that the experimentally observed uniform susceptibility data is inconsistent with the weakly coupled dimer picture of Marini and Khomskii. The model proposed by Pickett can, with appropriate choice of parameters, lead to an explanation for the observed gap and uniform susceptibility. The resulting agreement with experiments is of a similar quality to previously studied models. We argue that this new model is best distinguished from previous ones by neutron or Raman scattering experiments, via the location of the excitation minimum in the Brillouin zone and by the possible existence or non-existence of sharply defined singlet excitations.
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