Thermodynamic properties of seven gaseous halogenated hydrocarbons from acoustic measurements: CHClFCF3, CHF2 CF3, CF3 CH3, CHF2CH3, CF3CHFCHF2, CF3CH2CF3, and CHF2CF2CH2F

Measurements of the speed of sound in seven halogenated hydrocarbons are presented. The compounds in this study are 1-chloro-1,2,2,2-tetrafluoroethane (CHClFCF₃ or HCFC-124), pentafluoroethane (CHF₂ CF₃ or HFC-125), 1,1,1-trifluoroethane (CF₃CH₃ or HFC-143a), 1,1-difluoroethane (CHF₂CH₃ or HFC-152a), 1,1,1,2,3,3-hexafluoropropane (CF₃CHFCHF₂ or HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (CF₃CH₂CF₃ or HFC-236fa), and 1,1,2,2,3-pentafluoropropane (CHF₂CF₂CH₂F or HFC-245ca). The measurements were performed with a cylindrical resonator at temperatures between 240 and 400 K and at pressures up to 1.0 MPa. Ideal-gas heat capacities and acoustic virial coefficients were directly deduced from the data. The ideal-gas heat capacity of HFC-125 from this work differs from spectroscopic calculations by less than 0.2% over the measurement range. The coefficients for virial equations of state were obtained from the acoustic data and hard-core square-well intermolecular potentials. Gas densities that were calculated from the virial equations of state for HCFC-124 and HFC-125 differ from independent density measurements by at most 0.15%, for the ranges of temperature and pressure over which both acoustic and Burnett data exist. The uncertainties in the derived properties for the other five compounds are comparable to those for HCFC-124 and HFC-125.     

Low-cost testing of high-density logic components

The evolution of a testing method and architecture of a logic-device tester to be used for the next generation of IBM's high-density CMOS ASIC (application-specific integrated circuit) logic components is described. The tester's design is based on the architecture of an existing IBM memory tester rather than on a conventional logic-tester design. The testing strategy calls for boundary-scan in each component design, built-in self-test logic within embedded memory arrays, and the use of weighted random-pattern logic testing. The development of the tester hardware is discussed, and capital costs of the new tester are compared with those of other approaches     

Structure in thin superfluid helium films

Precision measurements of third sound in atomically thin⁴He films on Ne, Ar, and CO₂ substrates reveal a periodic structure not corresponding to whole layers. Treating the He film as an incompressible, continuous fluid, the data indicate that the chemical potential has a contribution proportional to l^–6, where l is the He coverage in layers, which is modulated at intervals of 0.62±0.04 layers and which weakens the van der Waals potential. Alternatively the data indicates the existence in the film of a damped smectic density wave with a 0.54±0.40 layer periodicity.     

Effect of mechanical design of the suspension on dynamic loading process

In designing a load/unload system utilized in hard disk drives, necessary care needs to be taken to ensure that the slider does not damage the disk surface during loading and unloading processes. However, a small deviation in the design point of the preload between the load-dome and flexure can lead to undesirable loading processes resulting in an adverse number of slider/disk contacts. In this study, we show that if the preload between the load-dome and flexure is too low, the slider can oscillate causing the corners of the slider to contact the disk multiple times even though the slider is a few microns away from the disk. In addition, the slider can be sucked down towards the disk resulting in a complete separation of the load-dome from the flexure assembly leading to uncontrolled loading conditions. This separation occurs while the suspension is still on the ramp, and thus no preload is exerted on the slider immediately following the separation. Consequently, the slider flies at a flying height higher than the design point until the gap between the load-dome and flexure closes. Hence, the suspension must be carefully designed to suppress slider oscillation and to ensure that the load-dome does not separate during the loading process.     

Application of analytical techniques to stress relaxation experiments in commercial zinc

Stress relaxation is a simple test which offers the means for evaluating the deformation dynamics of materials. The main shortcoming of this test is that it requires a highly stable testing machine having small relaxation effects. In this article, stress relaxation tests are reported that were performed on commercial zinc at room temperature. The results were analyzed using Hart’s method and Li’s equation. Hart’s method shows that it is not possible to find a unique family of curves of stress as a function of the strain rate and, therefore, a mechanical equation of state. It is also shown that application of Li’s method always gives a straight line in the logarithm of stress-ratevs logarithm of time, even though a mechanical equation of state does not exist. The occurrence of parameters with physically unreal values when applying Li’s equation is shown to be a consequence of an inadequate range of data. A formula is given for the experimental time required to satisfactorily apply Li’s method.     

Contribution of rpoB mutations to development of rifamycin cross-resistance in Mycobacterium tuberculosis

The contributions of 23 insertion, deletion, or missense mutations within an 81-bp fragment of rpoB, the gene encoding the beta-subunit of the DNA-dependent RNA polymerase of Mycobacterium tuberculosis, to the development of resistance to rifamycins (rifampin, rifabutin, rifapentine, and KRM-1648) in 29 rifampin-resistant clinical isolates were defined. Specific mutant rpoB alleles led to the development of cross-resistance to all rifamycins tested, while a subset of mutations were associated with resistance to rifampin and rifapentine but not to KRM-1648 or rifabutin. To further study the impact of specific rpoB mutant alleles on the development of rifamycin resistance, mutations were incorporated into the rpoB gene of M. tuberculosis H37Rv, contained on a mycobacterial shuttle plasmid, by in vitro mutagenesis. Recombinant M. tuberculosis clones containing plasmids with specific mutations in either codon 531 or 526 of rpoB exhibited high-level resistance to all rifamycins tested, whereas clones containing a plasmid with a mutation in codon 516 exhibited high-level resistance to rifampin and rifapentine but were susceptible to both rifabutin and KRM-1648. These results provided additional proof of the association of specific rpoB mutations with the development of rifamycin resistance and corroborate previous reports of the usefulness of rpoB genotyping for predicting rifamycin-resistant phenotypes.     

Prevalence, course, and predictors of multiple problem behaviors among gay and bisexual male adolescents.

Multiple problem behaviors, stress, and personal resources were assessed over 2 yrs among 136 mainly Black and Hispanic gay and bisexual male adolescents (aged 14–19 yrs). Whereas sexual risk acts, substance abuse, conduct problems, and emotional distress were common, the risk acts did not form a multiple problem behavior cluster, compared with previous findings with heterosexual youths. Problem behaviors were stable over time: Only 20–30% of the youths changed their pattern of problem behaviors over 2 yrs. For each individual, the pattern of change in one behavior problem was not related to patterns of change in other problem behaviors over 2 yrs. At baseline, personal resources were associated with less alcohol use and emotional distress, and stress was associated with delinquent behaviors. The pattern of results was similar whether youths labeled themselves as gay or bisexual, suggesting that problem behaviors among mainly Black and Hispanic gay and bisexual youths may follow different developmental pathways than among heterosexual youths. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Low-energy electron-enhanced etching of HgCdTe

Low-energy electron-enhanced etching (LE4) is applied to HgCdTe to eliminate ion-induced surface damage. First, LE4 results for patterned samples are illustrated. The LE4 mechanism is understood from a mechanistic study in terms of three etch variables: direct current (DC) bias, gas composition, and sample temperature. For this paper, the effects of DC bias (electron energy) and gas composition (CH₄ concentration) are summarized qualitatively, followed by quantitative evidence. Etch rate, the amount of polymer, surface stoichiometry, and surface roughness have specific relations with each etch variable under competition between pure LE4 and polymer deposition.     

Genomic imprinting in testicular germ cell tumours

Genomic imprinting refers to the parental origin-specific functional difference between the paternally and maternally-derived mammalian haploid genome. Normal embryogenesis depends on the presence of both a paternal and a maternal copy of particular chromosomal regions, containing the so-called imprinted genes. Genomic imprinting is established somewhere in the maturation from a primordial germ cell to a mature gamete, either spermatid or oocyte. We discuss the value of testicular cancers, especially those derived from the germ cell lineage, as a model to study erasement of the biparental pattern of genomic imprinting as present in the zygote and establishment of the paternal pattern during spermatogenesis. In addition, we will present data on the presence of X-inactivation in these cancers.