A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.     

The atmospheric water vapor continuum below 300 GHz

Absolute attenuation rates due to water vapor and moist nitrogen have been measured in the laboratory at 138 GHz, 282 and 300 K, pressures up to 1.5 atm, and relative humidities from 80 to 100 percent. The computer-controlled measuring system is comprised of a millimeter wave resonance spectrometer (0.15 km effective path length) and a humidity simulator. Several shortcomings of earlier measurement attempts have been rectified. The data are interpreted as a water vapor continuum spectrum consisting of two terms, namely strong self-broadening (H₂O?H₂O) plus foreign-gas-broadening (H₂O?N₂) contributions. Implications of the new results for modeling atmospheric EHF window transparencies and for revising established H₂O line broadening theory are discussed.     

Rumen volatile fatty acid molar proportions,rumen epithelial gene expression,and blood metabolite concentration responses to ruminally degradable starch and fiber supplies

The objective of this work was to characterize rumen volatile fatty acid (VFA) concentrations, rumen epithelial gene expression, and blood metabolite responses to diets with different starch and fiber sources. Six ruminally cannulated yearling Holstein heifers (body weight = 330 ± 11.3 kg) were arranged in a partially replicated Latin square experiment with 4 treatments consisting of different starch [barley (BAR) or corn (CRN)] and fiber [timothy hay (TH) or beet pulp (BP)] sources. Treatments were arranged as a 2 × 2 factorial. Beet pulp and TH were used to create relative changes in apparent ruminal fiber disappearance, whereas CRN and BAR were used to create relative changes in apparent ruminal starch disappearance. Each period consisted of 3 d of diet adaptation and 15 d of dietary treatment. In situ disappearance of fiber and starch were estimated from bags incubated in the rumen from d 10 to 14. From d 15 to 17, rumen fluid was collected every hour from 0500 to 2300 h. Rumen fluid samples were pooled by animal/period and analyzed for pH and VFA concentrations. On d 18, 60 to 80 papillae were biopsied from the epithelium and preserved for gene expression analysis. On d 18, one blood sample per heifer was collected from the coccygeal vessel. In situ ruminal starch disappearance rate (7.30 to 8.72%/h for BAR vs. 7.61 to 10.5%/h for CRN) and the extent of fiber disappearance (22.2 to 33.4% of DM for TH vs. 34.4 to 38.7% of DM for BP) were affected by starch and fiber source, respectively. Analysis of VFA molar proportions showed a shift from propionate to acetate, and valerate to isovalerate on TH diets compared with BP. Corn diets favored propionate over butyrate in comparison to BAR diets. Corn diets also had higher molar proportions of valerate. Expression of 1 gene (SLC9A3) were increased in BP diets and 2 genes (BDH1 and SLC16A4) tended to be increased in TH diets. Plasma acetate demonstrated a tendency for a starch by fiber interaction with BAR-BP diets having the highest plasma acetate, but other metabolites measured were not significant. These results suggest that TH has the greatest effect on shifts in VFA molar proportions and epithelial transporters, but does not demonstrate shifts in blood metabolite concentrations.     

Moist-air attenuation at 96 GHz over a 21-km line-of-sight path

A propagation experiment at 96 GHz over a line-of-sight (LOS) path provided data on attenuation characteristics of atmospheric water vapor. Two consecutive time periods (three days in May and 1.5 days in August 1986) with a total of about 100 h of data on signal level and meteorological conditions were analyzed with respect to absolute humidity (3-21 g/m³) and temperature (4-32°C) variations. Experimental details, the data analysis, and a comparison with model predictions are discussed. The validity of the millimeter-wave propagation model is considered and it is concluded that the field experiment tends to uphold the validity of this model at 96 GHz     

Palomar Receive Terminal (PRT) for the Mars Laser Communication Demonstration (MLCD) Project

Significant technological advances were made toward utilizing the Hale telescope for receiving the faint laser communication signals transmitted from an optical transceiver on a spacecraft orbiting Mars. The so-called Palomar receive terminal design, which would have supported nominal downlink data rates of 1-30 Mbps, is described. Testing to validate technologies for near-Sun (3deg from edge of solar disc) daytime operations is also discussed. Finally, a laboratory end-to-end link utilizing a 64-ary pulse-position modulated photon-counting receiver and decoder that achieved predicted near-capacity (within 1.4 dB) performance is described.     

Chromosome 18 pairing behavior in human trisomic oocytes. Presence of an extra chromosome extends bouquet stage

Little is known about the first meiotic prophase stages in the human female because these occur during fetal life, and only a few studies have addressed aneuploid human oocytes. In this paper, the synaptic process in the meiotic prophase in three 47, XX+18 cases is analyzed. A complete study of the dynamics of centromeres and telomeres, cohesin core and synapsis development in aneuploid female meiosis was performed. Investigation of chromosome dynamics in prophase of trisomy 18 oocytes show that these events follow the major patterns seen earlier in euploid oocytes. However, there is a significant delay in the resolution of bouquet topology which could relate to the presence of a surplus chromosome 18 axial element in zygotene oocytes. Pachytene oocytes displayed normal synapsis among the three chromosome 18s. However, in some oocytes the surplus chromosome 18 core was aligned to the bivalent 18. As ataxia telangiectasia and Rad3 related kinase (ATR) has been described as a marker for late-pairing chromosomes in mice, ATR distribution was analyzed in human meiocytes--spermatocytes, euploid oocytes and trisomic oocytes. In contrast to the observations made in mice, no preferential staining for late-pairing chromosomes was observed in humans. In the cases studied, bivalent synapses progressed as in a normal ovary, contrasting with the hypothesis that a surplus chromosome can modify pairing of other chromosomes.     

Variability of EHF air refractivity with respect to temperature, pressure, and frequency

EHF transfer properties of air are expressed by a complex refractivityN, yielding phase dispersion and attenuation due to the microwave spectrum of oxygen. Based upon an experimetally verified theory (Rosenkranz band shape), the variability ofNwith respect to temperature, pressure, and frequency variations is analyzed across the 40 to 140 GHz band for atmospheric conditions up to 40 kilometers in altitude (300-200degK, 760-5 torr). The discussion centers on the usefulness of such information when treating problems of possible propagation limitations imposed by turbulent air and of remote sensing atmospheric states.     

Application of the material force method to isotropic continuum damage

 The objective of this work is the exploitation of the notion of material forces in computational continuum damage mechanics. To this end we consider the framework of isotropic geometrically non–linear continuum damage and investigate the spatial and material settings that lead to either spatial or material forces, respectively. Thereby material forces essentially represent the tendency of material defects to move relative to the ambient material. In this work we combine an internal variable approach towards damage mechanics with the material force method. Thus the appearance of distributed material volume forces that are conjugated to the damage field necessitates the discretization of the damage variable as an independent field in addition to the deformation field. Consequently we propose a monolithic solution strategy for the corresponding coupled problem. The underlying kinematics, strong and weak forms of the coupled problem will be presented and implemented within a standard Galerkin finite element procedure. As a result in particular global discrete nodal quantities, the so–called material node point (surface) forces, are obtained and are studied for a number of computational examples. Received: 19 August 2002 / Accepted: 16 October 2002