Depletion forces near a soft surface

We investigate excluded-volume effects in a bidisperse colloidal suspension near a flexible interface. Inspired by a recent experiment by Dinsmore et al. (Phys. Rev, Lett. 80, 409 (1998)), we study the adsorption of a mesoscopic bead on the surface and show that depletion forces could in principle lead to particle encapsulation. We then consider the effect of surface fluctuations on the depletion potential itself and construct the density profile of a polymer solution near a soft interface. Surprisingly we find that the chains accumulate at the wall, whereas the density displays a deficit of particles at distances larger than the surface roughness. This non-monotonic behavior demonstrates that surface fluctuations can have major repercusions on the properties of a colloidal solution. On average, the additional contribution to the Gibbs adsorbance is negative. The amplitude of the depletion potential between a mesoscopic bead and the surface increases accordingly.Comment: 10 pages, 5 figure

Computer Assisted Determination of the Ionization Constants of an Unusual Dibasic Acid

The ionization constants for an unusual keto ester were determined by examination of the complex visible-UV absorption spectra of the monobasic salt. Interpretation of changes with pH of the spectra at four different wave lengths required an estimate of 12 molar absorbancies and two ionization constants. A computer program permitted progressive selection of best values. The ratio of K1 to K2 for this acid is exceptionally high and exceeds that for any other acid for which we have found data

An efficiency upper bound for inverse covariance estimation

We derive an upper bound for the efficiency of estimating entries in the inverse covariance matrix of a high dimensional distribution. We show that in order to approximate an off-diagonal entry of the density matrix of a $d$-dimensional Gaussian random vector, one needs at least a number of samples proportional to $d$. Furthermore, we show that with $n \ll d$ samples, the hypothesis that two given coordinates are fully correlated, when all other coordinates are conditioned to be zero, cannot be told apart from the hypothesis that the two are uncorrelated.Comment: 7 Page

The Impact of The Initial Surface Reconstruction on Heteroepitaxial Film Growth and Defect Formation

While it is well known that growth conditions such as temperature greatly affect defect incorporation in thin films, less is known about the direct effects of the surface reconstruction. In this work, we examine the effect of the initial surface reconstruction on defect incorporation in GaSb/GaAs(001) lattice mismatched films. The stress built up in GaSb films grown on As-terminated and Sb-terminated GaAs was monitored during film growth and shows that the total relaxation is similar in both films along the [110], but lower on the Sb-terminated surface along the . These differences can be understood by examining the ability for the two surface terminations to accommodate strain. The resulting films show that the density of 3D islands is lower for the Sb-terminated surfaces, and that lattice mismatch strain is further accommodated by a 5° tilt. In contrast, the As-terminated surface contains both stacking faults and misfit dislocations. These results demonstrate the possibility to engineer specific defects into films by controlling the starting surface of film growth

Regulation of Meiotic Cohesion and Chromosome Core Morphogenesis during Pachytene in Drosophila Oocytes

During meiosis, cohesion between sister chromatids is required for normal levels of homologous recombination, maintenance of chiasmata and accurate chromosome segregation during both divisions. In Drosophila, null mutations in the ord gene abolish meiotic cohesion, although how ORD protein promotes cohesion has remained elusive. We show that SMC subunits of the cohesin complex colocalize with ORD at centromeres of ovarian germ-line cells. In addition, cohesin SMCs and ORD are visible along the length of meiotic chromosomes during pachytene and remain associated with chromosome cores following DNase I digestion. In flies lacking ORD activity, cohesin SMCs fail to accumulate at oocyte centromeres. Although SMC1 and SMC3 localization along chromosome cores appears normal during early pachytene in ord mutant oocytes, the cores disassemble as meiosis progresses. These data suggest that cohesin loading and/or accumulation at centromeres versus arms is under differential control during Drosophila meiosis. Our experiments also reveal that the alpha-kleisin C(2)M is required for the assembly of chromosome cores during pachytene but is not involved in recruitment of cohesin SMCs to the centromeres. We present a model for how chromosome cores are assembled during Drosophila meiosis and the role of ORD in meiotic cohesion, chromosome core maintenance and homologous recombination

Identification of proteins binding specifically to the 3′-untranslated region of granulocyte/macrophagecolony stimulating factor mRNA

The 3′-untranslated region of granulocyte/macrophage colony-stimulating factor (GM-CSF) mRNA contributes to the post-transcriptional regulation of gene expression. Degradation is partly mediated by adenosine-uridine-rich sequence elements (ARE), which serve as binding sites for specific proteins. Stabilization of RNA by phytohemagglutinin and concanavalin A treatment is dependent on regulatory sequence elements upstream of ARE. We have performed northwestern blot and filter binding assays using cell extracts and RNA sequences containing or lacking ARE. Murine and human T cell extracts (EL-4 and Jurkat) yielded two specific proteins of 93 and 94 kDa, respectively, that were binding to sequences upstream of ARE. Within this region, the human and murine RNA do not share any obvious sequence identity, yet both are target sites for the binding proteins. The smallest RNA fragments protected by the proteins from RNase A digestion, were 44 in the murine, and 38 ribonucleotides long in the human sequence. The binding activity of the 94 kDa protein derived from human Jurkat cells could be enhanced by phytohemagglutinin. The interaction with regulatory mRNA sequences and the responsiveness to phytohemagglutinin suggests that the proteins are involved in controlling GM-CSF mRNA turnove

Growth performance and metabolic changes in lambs and steers after mild nutritional restriction

Two trials investigating compensatory growth are reported in which lambs and young cattle were placed on either a continuous (C) or a discontinuous (RR) growth path. RR animals were subjected to a phase of restricted feeding and then realimented at an equivalent level of feeding to C animals over the same live-weight range. Eight 4-month-old lambs and 30 9-month-old Swiss Brown steers were used. The restriction (I) and realimentation (II) phase covered the live-weight ranges 23-32 kg and 32-44 kg respectively in tho lamb trial and 236-310 kg and 310-460 kg respectively in the steer trial. Fifty-six total energy balances were made with lambs using open-circuit respiration calorimetry. Fifty determinations of diet digestibility and N balance were made with steers. Lambs received a pelleted concentrate diet and, except for restrictively fed steers which received hay alone, steers were offered a diet based on maize silage. The restriction phase of RR lambs and RR steers was longer, and the daily ME intake and daily live-weight gains were significantly lower than those of the C animals. Compared with C lambs a marked reduction in methane production of RR lambs occurred during feed restriction which persisted throughout realimentation. During recovery realimented lambs gained non-significantly, but realimented steers significantly, more than C animals from a similar ME intake and required less ME/kg daily live-weight gain. Realimented lambs retained more protein at the start of recovery compared with C lambs but both C and realimented steeis retained similar amounts of nitrogen. Indirect evidence is presented that suggests improved utilization of ME for protein deposition, at least at the start of realimentation. Although the animals on the discontinuous growth path (RR) took longer to reach slaughter weight, their total intake of gross energy and overall energy conversion ratio (MJ ME/kg live-weight gain) was similar to those of animals on the continuous growth path (C