Nonlinear behavior of vibrating molecules on suspended graphene waveguides

Suspended graphene waveguides were deposited on micron-scale periodic metal (plasmonic) structures. Raman scattering of test molecules (B. Megaterium), deposited on the waveguides' surface, exhibited azimuthal cycles upon rotation: at these micron scales, spontaneous Raman ought to be independent of phase matching conditions. In addition, we observed angular-selective quadratic intensity dependence contrary to the typical linear behavior of spontaneous Raman. The effects were observed at very modest pump laser intensities (<10 MW/cm2 at the sample surface, oftenly used in Raman experiments). We attributed these observations to nonlinear coupling between the vibrating molecules and surface plasmon polariton (SPP) modes at the molecular vibration frequency. It was assessed that the polariton mode propagates through fairly long distances (over 100 microns).Comment: 18 pages; 3 figures; a journal pape

Graphene-coated substrates for biochemical and optoelectronic applications

Graphene - monolayer or a few layers of graphite -- has proven to possess remarkable properties: large thermal conductivity, mechanical robustness, two-dimensional ultra large electronic mobility, chemical inertness and biochemical compatibility. Realization of some applications has been impeded by lack of a large area deposition method. By using a novel methodology to deposit graphene on solid and perforated substrates, various optoelectronic and biochemical elements have been demonstrated in this thesis: (1) graphene based transistors were fabricated and their characteristics were assessed. The mobility for such transistors exceeded 5000 cm2/V·s, much larger than their silicon based counterparts. Such attribute opens up new potential application in the field of very large scale integration (VLSI). (2) In parallel to vacuum tubes, where accelerated electrons are retained by a biased screen, a graphene based retaining electrode, placed in a wet-cell battery has stopped the battery’s current. In that respect, graphene proved to be a good ionic screening electrode because it does not oxidize easily. Applications could be in the field of ionic transistors and special electrochemical cells. (3) As surface pl asmon waveguides enter the electronic circuitry, surface plasmon sources are required. Graphene based surface pl asmons lasers were fabricated and characterized. Their attributes, illustrated by operational threshold, gain, spectral line narrowing and feedback at 630 nm all alluded to the action of a laser. Such, local pl asmonic sources may find applications in optoelectronic and sensor systems. (4) Infrared (IR) metal-mesh screens have been investigated as optical filters in the visible through the THz spectral region for astronomy and remote sensing applications. By interfacing these metal mesh screens with graphene, new spectroscopic platforms were fabricated. It has been shown that these platforms enhance I R and Raman signals of molecules and, specifically, signal of bio-species at the screens\u27 surface. Biochemical sensing applications are envisioned. (5) Finally, the Raman spectra of molecules, deposited on graphene-coated nano-hole arrays have been investigated. It has been shown that these platforms were able to intensify such Raman signals, significantly. Potential usage of such platforms as biochemical sensors is envisioned

Ruling out Strongly Interacting Dark Matter-Dark Radiation Models from Joint Cosmic Microwave Background-Quasar Observations

The cold dark matter (CDM) paradigm provides a remarkably good description of the Universe's large-scale structure. However, some discrepancies exist between its predictions and observations at very small sub-galactic scales. To address these issues, the consideration of a strong interaction between dark matter particles and dark radiation emerges as an intriguing alternative. In this study, we explore the constraints on those models using joint observations of Cosmic Microwave Background (CMB) and Quasars with our previously built parameter estimation package CosmoReionMC. At 2-$\sigma$ confidence limits, this analysis rules out all strongly interacting Dark Matter - Dark Radiation models proposed to date, representing the most stringent constraint on those models to the best of our knowledge. Future research using a 21-cm experiment holds the potential to reveal stronger constraints or uncover hidden interactions within the dark sector.Comment: Submitted to MNRAS Letter

Clustering and physical properties of the star-forming galaxies and AGN: does assembly bias have a role in AGN activity?

We compare the spatial clustering and physical properties of the active galactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar mass using a volume limited sample from the Sloan Digital Sky Survey (SDSS). The analysis of the two-point correlation function shows that the AGN are more strongly clustered than the SFG. The closer proximity to the $5^{th}$ nearest neighbour for the AGN than that for the SFG indicates that AGN prefer the denser regions. We compare the distributions of the $(u-r)$ colour, star formation rate (SFR), D$4000$ and concentration index of the AGN and SFG after matching their stellar mass distributions. The null hypothesis can be rejected at $>99.99\%$ confidence level in each case. The comparisons are also carried out at different densities. The differences persist at the same significance level in both the high and low density regions, implying that such differences do not originate from the variations in the density. Alternatively stated, the AGN activity can be triggered in both the high and low density regions. An analysis of the correlations between the different physical properties at fixed stellar mass reveals that the anticorrelations of SFR with morphology, colour and recent star formation history are $2-3$ times stronger for the AGN than for the SFG. It suggests that the presence of a bulge and the availability of gas are the two most crucial requirements for AGN activity. We propose a picture where the galaxies at fixed stellar mass may have widely different assembly histories, leading to significant variations in bulge properties and cold gas content. Whether a galaxy of a given stellar mass can acquire the suitable conditions for AGN activity remains uncertain due to a broad diversity of assembly history. We conclude that AGN are stochastic phenomena owing to an underlying role of the assembly bias.Comment: 24 pages, 13 figures, 1 table, comments welcom

A comparative study between dexmedetomidine and propofol for maintaining depth of anesthesia in elective craniotomy: a prospective randomized double blind study

Background: The objective of present study was to assess the efficacy of dexmedetomidine over propofol in maintaining depth of anesthesia in patients undergoing elective craniotomy.Methods: Ninety patients of American Society of Anaesthesiologists (ASA) physical status 1 or 2, of either sex, with Glasgow Coma Score (GCS) 14 or 15, scheduled for elective craniotomy, were allocated in two groups, Group D and Group P. Each group consisted of 45 patients. Anesthesia was induced with propofol and maintained with nitrous oxide in oxygen, atracurium and intermittent fentanyl. Patients in Group D received continuous infusion of dexmedetomidine 0.4 µg/kg/hour which was started after induction and stopped after closure of dura in and patients in Group P received continuous infusion of propofol 100 µg/kg/min in same manner. Heart Rate (HR), mean arterial pressure (MAP), and bispectral index (BIS) were recorded and compared at specific time points which are known to have hemodynamic alterations throughout the intraoperative period.Results: Dexmedetomidine was comparable and even better (after intubation p 0.02, head pin fixation p 0.00, opening of dura p &lt;0.00) than propofol in maintaining depth of anesthesia. It also attenuated HR and MAP at intubation, head pin fixation, skin incision, making of burr hole, opening of dura and at extubation (p 0.00). But Ramsay sedation score of patients after extubation in both groups did not differ significantly (p 0.36). No patient had recall.Conclusions: Dexmedetomidine is comparable with propofol in maintaining depth of anesthesia during elective craniotomy. It can be used as a sole anesthetic agent during craniotomy.

Optimal organization of surrogacy contracts and underinvestment

We develop a model of commercial gestational surrogacy in which a childless couple approaches a prospective surrogate, who is willing to gestate for the couple. The surrogate’s care is non-contractible. We show that if the surrogate doesn’t have any wealth, at the optimum, she is always found to put in sub-optimal effort. Put differently, the surrogate cannot be made a residual claimant and therefore eliciting first best care is never optimal. Therefore the paper, in a hidden action framework, formalizes this ‘inefficiency’ inherent in the Indian ‘rent-a-womb’ market

A study of prevalence of metabolic syndrome in patients with type 2 diabetes mellitus in a tertiary care referral hospital in West Bengal

Background: The terms "metabolic syndrome", "insulin resistance syndrome" and "syndrome X" are now used specifically to define a constellation of abnormalities that is associated with increased risk for the development of type 2 diabetes and atherosclerotic vascular disease. It is a state of chronic low grade inflammation with the profound systemic effects. Several organisations gave several criteria to diagnose it. Effective preventive approaches include lifestyle changes, primarily weight loss, diet, and exercise, the appropriate use of pharmacological agents to reduce the specific risk factors.Methods: A cross-sectional study was done to evaluate the co-morbidity profile of patients, with metabolic syndrome and correlate clinical manifestations with specific components or metabolic syndrome, at the OPD of Bankura Sammilani Medical College and Hospitals, West Bengal. American Association of Clinical Endocrinologists criteria were chosen for diagnosis.Results: 100 patients were recruited having type II diabetes mellitus. Most of the patients were male between 20-70 years and maximum was on oral hypoglycemic agent with app 40% patient was without any glycemic control. In comorbidities hypertension was highest, followed by coronary artery disease, hypothyroidism and cerebrovascular accident. Waist-hip ratio was highest in female. All of the patients were having some cardiac risk factor assessed by ECG, echocardiography and thread mill test.Conclusions: The data demonstrates that metabolic syndrome is extremely common among diabetic patients. Frequency was much higher in women than men. Obesity is a key element in causing the metabolic syndrome and this factor was also more common in women

An observational comparative study of different doses of azilsartan and with chlorthalidone combination in moderate hypertension

Background: High blood pressure (BP) is one of the significant non-communicable diseases that are of high prevalence in our country. Hypertension (HTN) is responsible cause of 57% of stroke and 24% of coronary heart disease deaths in India. Eight classes of medications are currently used in the treatment of hypertension. Azilsartan medoxomil is a newly added FDA approved drug to the ARB class of antihypertensive agents. azilsartan and chlorthalidone combination is also got the FDA approval. There is limited study in between these two groups regarding efficacy especially in rural Bengal.Methods: A prospective observational study was done in medicine OPD of Bankura Sammilani Medical College for twelve weeks with two groups that are azilsartan (80mg) and fixed dose combination of azilsartan (40mg) plus chlorthalidone (12.5mg) in the age group of 18 to 55years of moderate hypertensive patients. Change of heart rate was assessed as safety parameter.Results: It was found that both the group of drugs are very much effective in lowering blood pressure constantly in respect of both systolic and diastolic BP but azilsartan monotherapy in high dose reduce systolic blood pressure slightly high. Significant change of heart rate was not seen with both the groups.Conclusions: Both the group was effective as well as safe in hypertensive patients

Magnetodielectric effect in nickel nanosheet-Na-4 mica composites

Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of Na-4 mica template. The specimens show magnetodielectric effect at room temperature with a change of dielectric constant as a function of magnetic field, the electric field frequency varying from 100 to 700 kHz. A decrease of 5% in the value of dielectric constant was observed up to a field of 1.2 Tesla. This is explained by an inhomogeneous two-component composite model as theoretically proposed recently. The present approach will open up synthesis of various nanocomposites for sensor applications.Comment: 11 pages, 7 figure

Sensing behaviour of some nanocomposite systems

Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystallites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique followed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO2, C2H5OH and NO2, respectively. The latter arose because of reduction/oxidation of Sn4+/Sn2+ species present at the shell layer of the nanostructures. Nickel nanosheets of thickness ~0.6 nm grown within the interlayer spaces of Na-4 mica crystallites showed a change of dielectric permittivity (5%) for an applied magnetic field of 1.2 Tesla. An inhomogeneous model was used to explain this behavior. Two dimensional CuO phase was grown within the channels of diameter ~5 nm of mesoporous SiO2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO3 nanoparticles of diameter ~25 nm having pores with diameter 10 nm showed multiferroic behavior which arose due to the presence of oxygen vacancies as a result of large surface area present. An M.D. parameter of 11% was found. Similarly mesoporous LiNbO3 of 10 nm diameter showed an M.D. parameter of ~4.5% at a magnetic field 1 Tesla. A giant magnetocapacitance effect with a value of 44% at 1.5 T was observed in nickel zinc ferrite (NZF) impregnated mesoporous silica. A magnetocapacitance of 51% at magnetic field 1.7 T was found in the case of nanocomposites comprising of iron ion containing silica based nanoglass and mesoporous silica. In the last two examples the behavior was explained on the basis of Catalan model of space-charge polarization with extracted values of magnetoresistance of the NZF and nanoglass phases being 58%