Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle

We study the distance dependence of the rate of electronic excitation energy transfer from a dye molecule to a metal nanoparticle. Using the spherical jellium model, we evaluate the rates corresponding to the excitation of l = 1, 2, and 3 modes of the nanoparticle. Our calculation takes into account both the electron-hole pair and the plasmon excitations of the nanoparticle. The rate follows conventional R^-6 dependence at large distances while small deviations from this behavior are observed at shorter distances. Within the framework of the jellium model, it is not possible to attribute the experimentally observed d^-4 dependence of the rate to energy transfer to plasmons or e-h pair excitations.Comment: 4 figure

The dynamics of loop formation in a semiflexible polymer

The dynamics of loop formation by linear polymer chains has been a topic of several theoretical/experimental studies. Formation of loops and their opening are key processes in many important biological processes. Loop formation in flexible chains has been extensively studied by many groups. However, in the more realistic case of semiflexible polymers, not much results are available. In a recent study (K. P. Santo and K. L. Sebastian, Phys. Rev. E, \textbf{73}, 031293 (2006)), we investigated opening dynamics of semiflexible loops in the short chain limit and presented results for opening rates as a function of the length of the chain. We presented an approximate model for a semiflexible polymer in the rod limit, based on a semiclassical expansion of the bending energy of the chain. The model provided an easy way to describe the dynamics. In this paper, using this model, we investigate the reverse process, i.e., the loop formation dynamics of a semiflexible polymer chain by describing the process as a diffusion-controlled reaction. We perform a detailed multidimensional analysis of the problem and calculate closing times for a semiflexible chain which leads to results that are physically expected. Such a multidimensional analysis leading to these results does not seem to exist in the literature so far.Comment: 37 pages 4 figure

Pulling a polymer out of a potential well and the mechanical unzipping of DNA

Motivated by the experiments on DNA under torsion, we consider the problem of pulling a polymer out of a potential well by a force applied to one of its ends. If the force is less than a critical value, then the process is activated and has an activation energy proportinal to the length of the chain. Above this critical value, the process is barrierless and will occur spontaneously. We use the Rouse model for the description of the dynamics of the peeling out and study the average behaviour of the chain, by replacing the random noise by its mean. The resultant mean-field equation is a nonlinear diffusion equation and hence rather difficult to analyze. We use physical arguments to convert this in to a moving boundary value problem, which can then be solved exactly. The result is that the time $t_{po}$ required to pull out a polymer of $N$ segments scales like $N^2$. For models other than the Rouse, we argue that $t_{po}\sim N^{1+\nu}$Comment: 11 pages, 6 figures. To appear in PhysicalReview

Synchronization from Disordered Driving Forces in Arrays of Coupled Oscillators

The effects of disorder in external forces on the dynamical behavior of coupled nonlinear oscillator networks are studied. When driven synchronously, i.e., all driving forces have the same phase, the networks display chaotic dynamics. We show that random phases in the driving forces result in regular, periodic network behavior. Intermediate phase disorder can produce network synchrony. Specifically, there is an optimal amount of phase disorder, which can induce the highest level of synchrony. These results demonstrate that the spatiotemporal structure of external influences can control chaos and lead to synchronization in nonlinear systems.Comment: 4 pages, 4 figure

A Randomized Controlled Trial of Glucose versus Amylase Resistant Starch Hypo-Osmolar Oral Rehydration Solution for Adult Acute Dehydrating Diarrhea

Background: Reduction of gross diarrhea rate in excess of that seen over time with intravenous therapy and appropriate antibiotics is not usually achieved by oral glucose-electrolyte rehydration therapy for cholera and cholera-like diarrheas. Methodology and Principal Findings: This prospective randomized clinical trial at a tertiary referral hospital in southern India was undertaken to determine whether amylase resistant starch, substituting for glucose in hypo-osmolar oral rehydration solution, would reduce diarrhea duration and weight in adults with acute severe dehydrating diarrhea. 50 adult males with severe watery diarrhea of less than three days' duration and moderate to severe dehydration were randomized to receive hypo-osmolar ORS (HO-ORS) or HO-ORS in which amylase resistant high amylose maize starch 50g/L substituted for glucose (HAMS-ORS). All remaining therapy followed standard protocol. Duration of diarrhea (ORS commencement to first formed stool) in hours was significantly shorter with HAMS-ORS (median 19, IQR 10-28) compared to HO-ORS (median 42, IQR 24-50) (Bonferroni adjusted P, P-adj < 0.001). Survival analysis (Kaplan-Meier) showed faster recovery from diarrhea in the HAMS-ORS group (P < 0.001, log rank test). Total diarrhea fecal weight in grams (median, IQR) was not significantly lower in the HAMS-ORS group (2190, 1160-5635) compared to HO-ORS (5210, 2095-12190) (P-adj = 0.08). However, stool weight at 13-24 hours (280, 0-965 vs. 1360, 405-2985) and 25-48 hours (0, 0-360 vs. 1080, 55-3485) were significantly lower in HAMS-ORS compared to HO-ORS group (Padj = 0.048 and P = 0.012, respectively). ORS intake after first 24 hours was lower in the HAMS-ORS group. Subgroup analysis of patients with culture isolates of Vibrio cholerae indicated similar significant differences between the treatment groups. Conclusions: Compared to HO-ORS, HAMS-ORS reduced diarrhea duration by 55% and significantly reduced fecal weight after the first 12 hours of ORS therapy in adults with cholera-like diarrhea

Tibial deformity correction by Ilizarov method

The case series illustrates the correction of bony deformities of the tibia through a percutaneous osteotomy and gradual distraction with the Ilizarov apparatus in order to restore shape and function of the lower limb. A total of 13 cases of tibial deformity which were gradually corrected by the Ilizarov method were included in the study. The plane and degree of deformity was calculated by Drorr Paley’s method. The tibial deformity was gradually corrected in all patients by the Ilizarov method. Hinges were appropriately placed usually at the level of deformity (CORA). In most of the cases percutaneous osteotomy was done at the level of CORA. In juxta-articular deformities, hinges were placed at the level of CORA but the osteotomy was done at different levels. The mean tibial varus in 12 patients was 24 degrees (range of 18 to 34 degrees) and one patient had a tibial valgus of 22 degrees which was corrected to restore a 90 degree medial proximal tibial angle. No healing problems in the regenerate except for one probable hypertrophic non-union. None of the patients with a tibial varus developed any neurological deficit or compartment syndrome following correction

On the atomic structure of cocaine in solution

Cocaine is an amphiphilic drug which has the ability to cross the blood–brain barrier (BBB). Here, a combination of neutron diffraction and computation has been used to investigate the atomic scale structure of cocaine in aqueous solutions. Both the observed conformation and hydration of cocaine appear to contribute to its ability to cross hydrophobic layers afforded by the BBB, as the average conformation yields a structure which might allow cocaine to shield its hydrophilic regions from a lipophilic environment. Specifically, the carbonyl oxygens and amine group on cocaine, on average, form ~5 bonds with the water molecules in the surrounding solvent, and the top 30% of water molecules within 4 Å of cocaine are localized in the cavity formed by an internal hydrogen bond within the cocaine molecule. This water mediated internal hydrogen bonding suggests a mechanism of interaction between cocaine and the BBB that negates the need for deprotonation prior to interaction with the lipophilic portions of this barrier. This finding also has important implications for understanding how neurologically active molecules are able to interact with both the blood stream and BBB and emphasizes the use of structural measurements in solution in order to understand important biological function.Peer ReviewedPostprint (author's final draft