Transport study of Berry's phase, the resistivity rule, and quantum Hall effect in graphite

Transport measurements indicate strong oscillations in the Hall-,$R_{xy}$, and the diagonal-, $R_{xx}$, resistances and exhibit Hall plateaus at the lowest temperatures, in three-dimensional Highly Oriented Pyrolytic Graphite (HOPG). At the same time, a comparative Shubnikov-de Haas-oscillations-based Berry's phase analysis indicates that graphite is unlike the GaAs/AlGaAs 2D electron system, the 3D n-GaAs epilayer, semiconducting $Hg_{0.8}Cd_{0.2}Te$, and some other systems. Finally, we observe the transport data to follow $B\times dR_{xy}/dB \approx - \Delta R_{xx}$. This feature is consistent with the observed relative phases of the oscillatory $R_{xx}$ and $R_{xy}$.Comment: 5 pages, 4 figure

Pulsar Scintillation and the Local Bubble

We present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 - 35 pc cm^-3 caried out using the Ooty Radio Telescope (ORT) at 327 MHz, to investigate the distribution of ionized material in the local interstellar medium. Observations were made during the period January 1993 to August 1995, in which the dynamic scintillation spectra of these pulsars were regularly monitored over 10 - 90 epochs spanning 100 days. Reliable and accurate estimates of strengths of scattering have been deduced from the scintillation parameters averaged out for their long-term fluctuations arising from refractive scintillation (RISS) effects. Our analysis reveals several anomalies in the scattering strength, which suggest tht the distribution of scattering material in the Solar neighborhood is not uniform. We have modelled these anomalous scattering effects in terms of inhomogeneities in the distribution of electron dnsity fluctuations in the local interstellar medium (LISM). Our model suggests the presence of a low density bubble surrounded by a shell of much higher density fluctuations. We are able to put constraints on geometrical and scattering properties of such a structure, and find it to be morphologically similar to the Local Bubble known from other studies.Comment: 35 pages, 12 figure

Long-Term Scintillation Studies of Pulsars: III. Testing Theoretical Models of Refractive Scintillation

Refractive interstellar scintillation (RISS) is thought to be the cause behind a variety of phenomena seen at radio wavelengths in pulsars and compact radio sources. Though there is substantial observational data to support several consequences of it, the quantitative predictions from theories have not been thoroughly tested. In this paper, data from our long-term scintillation study of 18 pulsars are used to test the predictions. The fluctuations of decorrelation bandwidth ($\nu_d$), scintillation time scale ($\tau_d$) and flux density (F) are examined for their cross-correlations and compared with the predictions. The theory predicts a strong correlation between $\nu_d$ and $\tau_d$, and strong anti-correlations between $\nu_d$ and F, and $\tau_d$ and F. For 5 pulsars, we see a reasonable agreement. There is considerable difficulty in reconciling the results for the rest of the pulsars. Our analysis shows the underlying noise sources can sometimes reduce the correlation, but cannot cause an absence of correlation. It is also unlikely that the poor flux correlations arise from a hitherto unrecognized intrinsic flux variations. For PSR B0834+06, which shows anomalous behaviour of persistent drift slopes, positive correlation is found between $\tau_d$ and the drift-corrected $\nu_d$. Many pulsars show an anti-correlation between $\nu_d$ and the drift slope, and this is in accordance with the simple models of RISS. The detections of correlated variations of observables and a reasonable agreement between the predicted and measured correlations for some pulsars confirm RISS as the primary cause of the observed fluctuations. However, the complexity seen with the detailed results suggests the necessity of more comprehensive theoretical treatments for describing refractive fluctuations and their correlations.Comment: 27 pages, 6 Figures, 6 Tables. Accepted for publication in The Astrophysical Journa

Renal and Electrolyte Disturbances in HIV infected patients

BACKGROUND & OBJECTIVES: HIV/AIDS patients may have renal involvement also, however, Indian data are sparse. The present study was done to find the prevalance of renal diseases in HIV/AIDS patients attending ART Centre, Govt. Rajaji hospital Madurai. METHODS: A previously designed proforma will be used to collect the demographic and clinical details of the patients. Two hundred patients will be selected randomly. All the patients will undergo detailed clinical evaluation, appropriate investigations such as CD4+ count, Blood sugar, Blood urea, serum creatinine, Serum electrolytes, urine routine and USG abdomen. The study group will be divided into two groups: Group A ART naive patients and Group B HIV patients on ART. RESULTS: About 60% of study population were in the age group of 21-40 years and 36% of study populalation were in the age group of 41-60 year. Around 62% of study population were ART NAIVE and 38% were on ART. Gender distribution is of around 65% male and 35% female. Blood urea and creatinine level was raised in 33 patients (16.5%) of study population, among them 9 patients (27%) on ART and 24 patients (73%) were ART NAÏVE. Around 45% patients have CD4 count between 200-500 and 32% patients have CD4 count 501-1000. Mean urea level in the study population was found to be 30.140 ; with a standard deviation of 15.372. Mean serum creatinine in the study population is 1.109 with a standard deviation of 0.618. Blood urea and creatinine levels are raised in ART naïve patients than patients on ART, p value were 0.038 and 0.047 respectively, it is statistically significant which indicates urea and creatinine level was higher in ART NAÏVE patients and lower in patients taking ART. Around 72 (36%) patients were found to be having hyponatremia. Mean serum sodium in the study population is 133.7 with a standard deviation of 7.199. Around 41 (20.5% ) patients were found to be having hypokalemia . Mean serum potassium in the study population is 3.892 with a standard deviation of 0.894. Serum sodium and potassium level was found to be decreased in more ART naïve patients than those on ART, p value were < 0.027 and < 0.015 respectively which is statistically significant and indicates Na+ and K+ level was significantly lower in ART NAÏVE patients compared to patients on ART. Proteinuria present in 33 patients (16.5%) of study population, among them 9 patients (27%) on ART and 24 patients (73%) were ART NAÏVE. Significant proteinuria was higher in ART NAÏVE patients and lower in patient taking ART. USG abdomen showed increased cortical echoes in 30 patients (15%) of study population, among them 7 patients (23%) on ART and 23 patients (77%) were ART NAÏVE. Renal cortical echoes were higher in ART NAÏVE patients and low occurence in patient taking ART. Cortico medullary differentiation was maintained in all patients. INTERPRETATION & CONCLUSIONS: Renal involvement seems to be common in Indian patients with HIV. Elevated Blood urea, serum creatinine and proteinuria could be an early marker of HIV associated renal lesions and screening for their presence may be beneficial. A low occurrence of renal involvement found in patients already on ART suggests some renoprotective effect of ART. Hyponatremia, hypokalemia and hyperkalemia are common electrolyte disorders in HIV infected patients. Among them hyponatremia and hypokalemia incidence is more in ART NAIVE patients than patient on ART. This indicates decreased incidence of electrolyte disturbances on patients on ART may be due to less oppurtunistic infections in them. The present findings need to be confirmed with further studies with larger sample size and prolonged period of follow up