Pair diffusion, hydrodynamic interactions, and available volume in dense fluids

We calculate the pair diffusion coefficient D(r) as a function of the distance r between two hard-sphere particles in a dense monodisperse suspension. The distance-dependent pair diffusion coefficient describes the hydrodynamic interactions between particles in a fluid that are central to theories of polymer and colloid dynamics. We determine D(r) from the propagators (Green's functions) of particle pairs obtained from discontinuous molecular dynamics simulations. At distances exceeding 3 molecular diameters, the calculated pair diffusion coefficients are in excellent agreement with predictions from exact macroscopic hydrodynamic theory for large Brownian particles suspended in a solvent bath, as well as the Oseen approximation. However, the asymptotic 1/r distance dependence of D(r) associated with hydrodynamic effects emerges only after the pair distance dynamics has been followed for relatively long times, indicating non-negligible memory effects in the pair diffusion at short times. Deviations of the calculated D(r) from the hydrodynamic models at short distances r reflect the underlying many-body fluid structure, and are found to be correlated to differences in the local available volume. The procedure used here to determine the pair diffusion coefficients can also be used for single-particle diffusion in confinement with spherical symmetry.Comment: 6 pages, 5 figure

Spacecraft redesign to reduce microphonic response of a VCO component

Reaction wheel vibration was found to induce out of specification sidebands on the carrier frequencies of some spacecraft components containing mechanical voltage control oscillators (VCOs). Concurrent investigations were performed to redesign the VCOs to reduce their response to the wheel vibration, and to design a reaction wheel isolation system to reduce the vibration input to the affected components. Component level tests indicated that both efforts provided viable solutions. The redesigned VCO will be incorporated into future spacecraft in the series, while affected spacecraft already in production will be retrofitted with the reaction wheel isolation system

The UARS and open data concept and analysis study

Alternative concepts for a common design for the UARS and OPEN Central Data Handling Facility (CDHF) are offered. Costs for alternative implementations of the UARS designs are presented, showing that the system design does not restrict the implementation to a single manufacturer. Processing demands on the alternative UARS CDHF implementations are then discussed. With this information at hand together with estimates for OPEN processing demands, it is shown that any shortfall in system capability for OPEN support can be remedied by either component upgrades or array processing attachments rather than a system redesign. In addition to a common system design, it is shown that there is significant potential for common software design, especially in the areas of data management software and non-user-unique production software. Archiving the CDHF data are discussed. Following that, cost examples for several modes of communications between the CDHF and Remote User Facilities are presented. Technology application is discussed

Topologically Robust Transport of Photons in a Synthetic Gauge Field

Electronic transport in low dimensions through a disordered medium leads to localization. The addition of gauge fields to disordered media leads to fundamental changes in the transport properties. For example, chiral edge states can emerge in two-dimensional systems with a perpendicular magnetic field. Here, we implement a "synthetic'' gauge field for photons using silicon-on-insulator technology. By determining the distribution of transport properties, we confirm the localized transport in the bulk and the suppression of localization in edge states, using the "gold standard'' for localization studies. Our system provides a new platform to investigate transport properties in the presence of synthetic gauge fields, which is important both from the fundamental perspective of studying photonic transport and for applications in classical and quantum information processing.Comment: 4.5 pages, 3 figures and supplementary materia

Excited states and electron transfer reactions of fullerenes

Since the discovery of carbon clusters in the laser ablated graphite vapours, fullerenes C60 and C70 have provided a constant source of excitement for the experimental and theoretical scientists alike. Their brilliant colours in solutions and three dimensional aromaticity has fascinated the photochemists. Our group has recently characterised singlet and triplet states of fullerenes using complementary twin techniques of laser f~ash ph~tolysis and electron pulse radiolysis. Singlet - singlet (S l→Sn) absorption spectra were studied in picosecond time domain and the rates of intersystem crossing were established. Triplet states were produced directly by photoexcitation in laser flash photolysis experimen~s and by energy transfer in pulse radiolysis. Triplet-triplet (Tl→Tn) spectra were characterised and rate constants for various triplet decay channels were measured. Fullerenes have low reduction potentials and form charge transfer (CT) complexes with good donors like aliphatic and aromatic amines. Exciting photochemical behaviour was observed on photoexcitation of the CT complexes which undergo ultrafast charge separation (CS) and charge recombination {CR) reactions. The dynamics of CS and CR reactions was studied in picosecond time scales in e60-diphenylamine and C60-triphenylamine systems. Using external heavy atom effect and solvent polarity variations, various steps in the CS and CR processes generating fullerene triplet on CR were elucidated. Recent results of complexing fullerenes with suitable hydrophilic cage like γ-cyclodextrin (CD) making C60 water soluble will also be presented. Excited state behaviour of fullerene complex in CD cage would be discussed

Cytological screening for cervical cancer in women of reproductive age group

Background: Cervical cancer is a malignant neoplasm arising from cells of cervix uteri. It is the second most common cancer among women worldwide, affecting about 16 per 1,00,000 women each year.Methods: A cross sectional study of 400 women of reproductive age group (21-49 years) attending Lady Goschen Hospital and KMC Hospital, Attavar, Mangalore was conducted, and women were screened for the presence of cervical cancer by Pap smear. The results were analyzed with respect to age distribution, age at marriage, parity, symptoms and per-speculum findings. Pregnant women and women with active infection of the genital tract were excluded from the study population.Results: The age range was 21 to 49 years. Mean age was 38.14 years. Of the 400 women, 398 were married and majority of these, 237 (59.5%), got married between 21-25 years. Menstrual irregularity was the most common presenting symptom, 150/400 (37.5%). Abnormal per speculum findings were seen in 102/400 (25.5%). 17 of 400 Pap smears were abnormal, of which 1 (0.25%) was AG-FN, 2 ASCUS (0.5%), 3 (0.75%) ASC-H, 1 (0.25%) LSIL, 7 (1.75%) HSIL and 3 (0.75%) SCC. Mean age for cancer cervix patients was 42.33 years.Conclusions: Pap smear screening, which appears to be the most feasible and affordable mode for control of carcinoma cervix in developing countries like India, should be carried out in all women of reproductive age group