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Frequency Increases (frequency + increase)
Selected AbstractsExperimental investigation of radiation properties of an antenna embedded in low permittivity thin-wire-based metamaterialMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2006Davor Bonefa Abstract Experimental results regarding the increase in directivity and gain of an antenna embedded in low-permittivity two-dimensional anisotropic thin-wire-based metamaterial are presented. As expected, increase in directivity and gain has been observed. The effect of main beam splitting with frequency increase, predicted by theoretical analysis, has been confirmed. The influence of the number of layers forming the metamaterial on the radiation pattern and gain has been investigated. Input impedance was measured both as a function of frequency and of the number of wire layers forming the metamaterial. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2581,2586, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21994 [source] Climate warming and the evolution of morphotypes in a reptileGLOBAL CHANGE BIOLOGY, Issue 2 2009VIRGINIE LEPETZ Abstract Climate warming is known to have effects on population dynamics through variations in survival, fecundity and density. However, the impacts of climate change on population composition are still poorly documented. Morphotypes are powerful markers to track changes in population composition. In the common lizard, Lacerta vivipara, individuals display two types of dorsal patterns: reticulated (R individuals) and linear (L individuals). We examined how local warming affected intrapopulation frequencies of these morphotypes across 11 years. We observed changes in morph frequency of dorsal patterns across years, paralleling the rise of spring temperatures. The proportion of R individuals increased with June temperatures in juveniles, yearlings, and adult males and females. Three mechanisms could explain these changes: phenotypic plasticity, microevolution and/or dispersal between populations. We investigated the ontogenetic determinism, fitness and recruitment rates associated with dorsal morphotypes. Dorsal pattern ontogeny showed temperature dependence but this relationship was not associated with the warming trend during this study. We found variation by morphotype in survival and clutch size, but these factors did not explain R frequency increases. Among all the parameters considered in this study, only a decrease of immigration, which was more pronounced in the L morphotype, could explain the change in population composition. To our knowledge, this provides the first evidence of the impact of climate warming on population composition due to its effects on immigration. [source] Comparison of suitable drought indices for climate change impacts assessment over Australia towards resource managementINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2008F. Mpelasoka Abstract Droughts have significant environmental and socio-economic impacts in Australia. This emphasizes Australia's vulnerability to climate variability and limitations of adaptive capacity. Two drought indices are compared for their potential utility in resource management. The Rainfall Deciles-based Drought Index is a measure of rainfall deficiency while the Soil-Moisture Deciles-based Drought Index is a measure of soil-moisture deficiency attributed to rainfall and potential evaporation. Both indices were used to assess future drought events over Australia under global warming attributed to low and high greenhouse gas emission scenarios (SRES B1 and A1F1 respectively) for 30-year periods centred on 2030 and 2070. Projected consequential changes in rainfall and potential evaporation were based on results from the CCCma1 and Mk2 climate models, developed by the Canadian Climate Center and the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) respectively. A general increase in drought frequency associated with global warming was demonstrated by both indices for both climate models, except for the western part of Australia. Increases in the frequency of soil-moisture-based droughts are greater than increases in meteorological drought frequency. By 2030, soil-moisture-based drought frequency increases 20,40% over most of Australia with respect to 1975,2004 and up to 80% over the Indian Ocean and southeast coast catchments by 2070. Such increases in drought frequency would have major implications for natural resource management, water security planning, water demand management strategies, and drought relief payments. Copyright © 2007 Royal Meteorological Society [source] Multifrequency integrated profiles of pulsarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Simon Johnston ABSTRACT We have observed a total of 67 pulsars at five frequencies ranging from 243 to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre-Wave Telescope in India and those at higher frequencies at the Parkes Telescope in Australia. We present profiles from 34 of the sample with the best signal-to-noise ratio and the least scattering. The general ,rules' of pulsar profiles are seen in the data; profiles get narrower, the polarization fraction declines and outer components become more prominent as the frequency increases. Many counterexamples to these rules are also observed, and pulsars with complex profiles are especially prone to rule breaking. We hypothesize that the location of pulsar emission within the magnetosphere evolves with time as the pulsar spins down. In highly energetic pulsars, the emission comes from a confined range of high altitudes, in the middle range of spin down energies the emission occurs over a wide range of altitudes whereas in pulsars with low spin-down energies it is confined to low down in the magnetosphere. [source] Surface trapping and leakage of low-frequency g modes in rotating early-type stars , I. Qualitative analysisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000R. H. D. Townsend A qualitative study of the surface trapping of low-frequency non-radial g modes in rotating early-type stars is undertaken within the Cowling, adiabatic and traditional approximations. A dispersion relation describing the local character of waves in a rotating star is derived; this dispersion relation is then used to construct propagation diagrams for a 7-M, stellar model, which show the location and extent of wave trapping zones inside the star. It is demonstrated that, at frequencies below a cut-off, waves cannot be fully trapped within the star, and will leak through the surface. Expressions for the cut-off frequency are derived in both the non-rotating and rotating cases; it is found from these expressions that the cut-off frequency increases with the rotation rate for all but prograde sectoral modes. While waves below the cut-off cannot be reflected at the stellar surface, the presence of a sub-surface convective region in the stellar model, owing to He ii ionization, means that they can become partially trapped within the star. The energy leakage associated with such waves, which are assigned the moniker virtual modes owing to their discrete eigenfrequencies, means that stability analyses which disregard their existence (by assuming perfect reflection at the stellar surface) may be in error. The results are of possible relevance to the 53 Per and SPB classes of variable star, which exhibit pulsation frequencies of the same order of magnitude as the cut-off frequencies found for the stellar model. It is suggested that observations either of an upper limit on variability periods (corresponding to the cut-off), or of line-profile variations owing to virtual modes, may permit asteroseismological studies of the outer layers of these systems. [source] Photoperiod at conception predicts C677T-MTHFR genotype: A novel gene-environment interactionAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2010Mark Lucock Data is presented, which suggest that the day length a woman experiences during the periconceptional period predicts the C677T-MTHFR genotype of her child. Logistic regression analysis involving 375 neonates born in the same geographical location within a three year period demonstrated that photoperiod (minutes) at conception predicts both genotype (P = 0.0139) and mutant allele carriage (P = 0.0161); the trend clearly showing that the 677T-MTHFR allele frequency increases as photoperiod increases. We propose a number of explanations, including a hypothesis in which a long photoperiod around conception decreases maternal systemic folate because of UVA induced dermal oxidative degradation of 5-methyl-H4folate, leading to a lower cellular 5,10-methylene-H4folate status. In this scenario, 5,10-methylene-H4folate would be more efficiently used for dTMP and DNA synthesis by 677T-MTHFR embryos than wildtype embryos giving the 677T-MTHFR embryos increased viability, and hence increasing mutant T-allele frequency. Alternate hypotheses include: increased seasonal availability of folate rich foods that genetically buffer any negative effect of 677T-MTHFR in embryos; seasonal oxidative stress lowering embryo-toxic homocysteine; an undefined hormonal effect of photoperiod on the neuroendocrine axis, which mediates genotype/embryo selection. The effect of photoperiod on genotype seems clear, but the speculative molecular mechanism underpinning the effect needs careful examination. Am. J. Hum. Biol., 2010. © 2010 Wiley-Liss, Inc. [source] Dual-gate AlGaN/GaN high-electron-mobility transistors with short gate length for high-power mixersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006K. Shiojima Abstract We have fabricated dual-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with a short gate on SiC substrates for use in high-power mixers and have measured the DC and up-conversion RF characteristics. A device with a T-shaped gate (0.15 µm × 300 µm) exhibits a maximum transconductance of 40 mS, an on-state breakdown voltage of over 30 V, and off-state breakdown voltage of 86 V. The maximum RF output power (PRFout) is 17 dBm, and the up-conversion gain is 7.5 dB at a frequency of 10 GHz when the bias point voltage is 30 V. As the local frequency increases from 2 to 10 GHz, PRFout and the gain decrease by only 2 and 2.6 dB, respectively. Shortening the gate was found to be effective in improving the frequency characteristics of a mixer at frequencies up to and including the X-band. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Aortic sclerosis,a marker of coronary atherosclerosisCLINICAL CARDIOLOGY, Issue 12 2004Yogendra Prasad M.D. Abstract Aortic valve sclerosis is defined as calcification and thickening of a trileaflet aortic valve in the absence of obstruction of ventricular outflow. Its frequency increases with age, making it a major geriatric problem. Of adults aged> 65 years, 21,29% exhibit aortic valve sclerosis. Incidence of aortic sclerosis increases with age, male gender, smoking, hypertension, high lipoprotein (Lp) (a), high low-density lipoprotein (LDL), and diabetes mellitus. Aortic valves affected by aortic sclerosis contain a higher amount of oxidized LDL cholesterol and show increased expression of metalloproteinases. Clinically, it can be suspected in the presence of soft ejection systolic murmur at the aortic area, normal split of the second heart sound, and normal volume carotid pulse, but it can be best detected by echocardiography. Aortic sclerosis may be accompanied by mitral annulus calcification up to 50% of cases. It is associated with an increase of approximately 50% in the risk of death from cardiovascular causes and the risk of myocardial infarction. The mechanism by which aortic sclerosis contributes to or is associated with increased cardiovascular risk is not known. Aortic sclerosis is associated with systemic endothelial dysfunction, and a small percentage of cases may progress to aortic stenosis. Lowering of LDL cholesterol by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to decrease progression of aortic valve calcification. Aortic sclerosis is not a mere benign finding. Once diagnosis of aortic sclerosis has been made, it should be considered a potential marker of coexisting coronary disease. Aggressive management of modifiable risk factors, especially LDL cholesterol lowering, may slow progression of the disease. [source] | |||||||||||||