Thermal conductivity and specific heat of thin-film amorphous silicon

We report the thermal conductivity and specific heat of amorphous silicon thin films measured from 5-300 K using silicon-nitride membrane-based microcalorimeters. Above 50 K the thermal conductivity of thin-film amorphous silicon agrees with values previously reported by other authors. However, our data show no plateau, with a low T suppression of the thermal conductivity that suggests that the scattering of long wavelength, low Q vibrations goes as Q2. The specific heat shows Debye-like behavior below 15 K, with theta(D) = 487 +/- 5 K, and is consistent with a very small contribution of tunneling states in amorphous silicon. Above 15 K, the specific heat deviates less from Debye behavior than does its crystalline allotrope, indicating no significant excess modes (boson peak) in amorphous silicon.

Specific heat of Ce0.8La0.2Al3 in magnetic fields: a test of the anisotropic Kondo picture

The specific heat C of Ce0.8La0.2Al3 has been measured as a function of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T field depresses the temperature of the peak by only 0.2 K, but strongly reduces its height. The corresponding peak in C/T shifts from 2.1 K at zero field to 1.7 K at 14 T. The extrapolated specific heat coefficient gamma = lim as T --> 0 of C/T increases with field over the range studied. We show that these trends are inconsistent with the anisotropic Kondo model.

Cloning of the crystalline cell wall protein gene of Bacillus licheniformis NM 105

A protein with a tetragonal pattern, defined as RS protein, was found on the wall surface of an alkaline phosphatase secretion-deficient mutant (NM 105) of Bacillus licheniformis 749/C. The protein was present on the wall surface of the exponential-growth-phase cells, but at the stationary growth phase it was overproduced and hypersecreted. This protein was precipitated to homogeneity from the culture fluid by 80% ammonium sulfate saturation and chilled acetone. The molecular mass of the protein was 98 kilodaltons, and it had a single subunit in a sodium dodecyl sulfate gel. Specific anti-RS antibody was generated in rabbits and used to immunolabel the RS protein on the cells at different growth phases. In early-exponential-growth-phase cells, the outside surface of the wall, the cytoplasm, and the inside surface of the cytoplasmic membrane were labeled. In stationary-growth-phase cells, the cytoplasm was poorly labeled, but the labeling on the outside surface of the wall was high. AB. licheniformis NM 105 gene library was made by using the lambda phage EMBL3. The RS protein expression from this gene library was detected by a modified autoradiographic procedure. One of the amplified RS protein-positive plaques (4213-1) containing recombinant DNA was chosen, and the restriction map of this DNA was prepared. The RS protein expressed in Escherichia coli NM 539 infected with 4213-1 recombinant phage had a lower molecular mass than the purified authentic RS protein. The 4.5-kilobase-pair (kbp) SalI-EcoRI fragment of the recombinant DNA was cloned in the shuttle plasmid pMK4 to construct pMK462, which was expressed in B. subtilis MI112 and produced the RS protein identical in molecular mass to the purified authentic RS protein. The RS protein expression was also demonstrated in cryosections of transformed E. coli and B. subtilis cells by immunoelectron microscopy. The 1.2-kbp SalI-HindIII and 1.8-kbp HindIII-HindIII recombinant DNA restriction enzyme fragments, respectively, from the right of the restriction map produced anti-RS antibody cross-reacting proteins. The expression of the 1.2-kbp SalI-HindIII DNA fragment cloned in pUC8 could be induced with isopropyl-beta-D-thiogalactopyranoside. The 1.8-kbp DNA restriction fragment hybridized with both the chromosomal DNA of strain NM 105 and the recombinant phage 4213-1 DNA. The RS gene expression was finally demonstrated in transformed E. coli 539 cells by in situ hybridization of frozen thin sections with the 1.8-kbp HindIII biotin-dATP probe and immunolabeling these with anti-biotin immunoglobulin G and protein A-gold.

Localization to the inner surface of the cytoplasmic membrane by immunoelectron microscopy of enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli

The phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli constitutes a major pathway for sugar translocation. It is composed of integral membrane proteins (enzyme II components) that recognize specific extracellular sugars as well as phosphocarrier proteins, one of which is called enzyme I. While enzyme I plays a role in energizing the enzyme II for sugar transfer, its precise cellular distribution had not previously been defined. This study was designed to elucidate the cellular location of this protein by immunoelectron microscopy. Enzyme I antibody bound to E. coli cryosections was visualized with protein A-gold. The gold particles in sections of wild-type E. coli were found primarily associated with the surface of the inner membrane. A strain of E. coli harboring a plasmid encoding the gene for enzyme I was also tested for its distribution of enzyme I. Consistent with the biochemically established overproduction of enzyme I, this strain showed an approximately 80-fold higher density of gold particles per unit cell volume than the wild-type cells. The substantial overproduction of immunoreactive enzyme I was associated with a significant (approximately 20-fold) increase in the amount of that protein bound to the inner membrane. In addition, a substantial fraction of the total enzyme I accumulated within a 60-nm-wide zone in the vicinity of the inner membrane. A model to explain the zonal distribution of enzyme I under conditions of overexpression of the protein is presented.

The structure of the chorion and associated surface filaments in Oryzias--evidence for the presence of extracellular tubules

The structure of the chorion with its associated surface filaments has been examined in Oryzias latipes using several techniques, including scanning and transmission electron microscopy, enzymatic digestion, and sodium dodecylsulfate-polyacrylamide gel electrophoresis. The chorion of the recently fertilized egg was found to be organized into three zones: an outer, fuzzy electron-lucent zone that was continuous over the surface of filaments, a middle, homogeneous electron-dense zone, and an inner zone of ten to 12 horizontal, fibrous lamellae. Two topographically distinct types of filaments were found on the chorionic surface: nonattaching and attaching. Nonattaching filaments showed a regular spatial distribution over the chorion with an interfilament distance of about 60-70 microns. Attaching filaments originated from a localized portion of the chorion and united with those of neighboring eggs to anchor the egg cluster to the gonoduct of the female. Both nonattaching and attaching filaments were morphologically regionalized into basal and distal segments. Internally, nonattaching and attaching filaments were constructed of unbranched, packed tubules with an average outside diameter of approximately 19.5 and 18.8 nm, respectively. Using the attaching filament for further study, it was determined by rotational analysis (Markham et al., '63) that the wall of each tubule was a cylinder composed of 14 globular subunits. Two structural types of attaching filaments were identified. The type I attaching filament was similar in internal organization to the nonattaching filament and consisted of only tubules. The type II attaching filament, however, showed a highly osmiophilic, electron-dense bar surrounded by packed tubules. Tubules of attaching filaments of the adult were resistant to the action of Triton X-100 and colchicine, but sensitive to a 0.1% protease solution. However, colchicine-treated ovary tissue showed an absence and pattern of disorganization of tubules at the periphery of developing filaments. Solubilized attaching filament samples electrophoresed on 7.5% polyacrylamide-SDS gels were resolved into a pair of Coomassie-blue-positive bands that comigrated with purified porcine brain tubulin. The apparent molecular weight of the attaching filament polypeptide was determined to be approximately 55,000 daltons. These data suggest that the extracellular, tubular components of attaching filaments (as well as nonattaching filaments) are proteinaceous and show properties similar to those of cytoplasmic microtubules. Tubular precursor material was electron-dense and appeared to originate in the cisternae of the rough endoplasmic reticulum of ovarian foll