Mass transfer cooling on a porous flat plate in carbon-dioxide and air streams

Mass transfer cooling on porous flat plate in carbon dioxide and air stream

Equilibrium temperatures of mass transfer cooled walls in high-speed flow of an absorbing-emitting gas

Equilibrium temperatures of mass transfer cooled walls in high speed flow of absorbing-emitting ga

Finite bounded expanding white hole universe without dark matter

The solution of Einstein's field equations in Cosmological General Relativity (CGR), where the Galaxy is at the center of a finite yet bounded spherically symmetrical isotropic gravitational field, is identical with the unbounded solution. This leads to the conclusion that the Universe may be viewed as a finite expanding white hole. The fact that CGR has been successful in describing the distance modulus verses redshift data of the high-redshift type Ia supernovae means that the data cannot distinguish between unbounded models and those with finite bounded radii of at least $c \tau$. Also it is shown that the Universe is spatially flat at the current epoch and has been at all past epochs where it was matter dominated.Comment: 11 pages, revised versio

Inter-specific variation in bud banks and flowering effort among semi-arid African savanna grasses

Population viability and productivity of grasses in southern African savannas are dependent upon both successful seed production and tiller recruitment from the belowground bud bank. Relative recruitment rates from buds versus seeds influence population dynamics, genetic diversity, and patterns of vegetation productivity. We assessed patterns in bud bank size and flowering effort in fourteen semi-arid savanna grass species in the Kalahari region of Botswana. There was high inter-specific variability and between-year variability in flowering effort (percentage of tillers flowering). Bud production (number of buds per tiller) exhibited high inter-specific variability, but was more consistent between-years than flowering effort. Relative allocation to flowering versus bud production varied with life history, with longer-lived perennial grasses showing higher bud production and lower flowering effort relative to shorter-lived grasses. Several species showed higher bud production and lower flowering effort in a wet year compared to a dry year, and grass species that are regularly grazed maintained significantly larger bud banks than non-grazed species. These differential demographic responses among co-occurring species suggest that environmental change in semi-arid savannas may alter the composition, relative abundances and diversity of grasses, and that the maintenance of a belowground bud bank is an important factor influencing their resiliency, their capacity to recover from grazing and/or drought, and their persistence and sustainability under changing environmental conditions. Meristem-limitation in species that maintain few viable buds may constrain their population viability under changing conditions in semi-arid savannas. (C) 2012 SAAB. Published by Elsevier B.V. All rights reserved

Performance of Multi-Beacon DGPS

Historically, maritime organizations seeking accurate shipboard positioning have relied upon some form of differential GNSS, such as DGPS, WAAS, or EGNOS, to improve the accuracy and integrity of the GPS. Groundbased augmentation systems, such as DGPS, broadcast corrections to the GPS signal from geographically distributed terrestrial stations, often called beacons. Specifically, pseudorange corrections for the GPS L1 C/A signal are computed at each reference site, then broadcast in the nearby geographic area using a medium frequency (approximately 300 kHz) communications link. The user then adds these corrections onto their measured pseudoranges before implementing a position solution algorithm. Within the United States, the U.S. Coast Guard operates 86 DGPS reference beacons. Similar DGPS systems are operated in Europe and elsewhere around the globe. While current DGPS receiver algorithms typically use one set of pseudorange corrections from one DGPS reference site (often the one with the “strongest” signal), many user locations can successfully receive two or more different DGPS broadcasts. This brings to mind obvious questions: “If available, how does one select the corrections to use from multiple sets of corrections?” and “Is it advantageous to combine corrections in some way?” We note that a number of factors might influence the effectiveness of any particular station’s corrections. Some of these refer to the effectiveness of the communications link itself, including concerns about interference from other beacons (skywave interference from far-away beacons on similar frequencies, a notable problem in Europe) and self-interference (skywave fading). Other factors refer to the accuracies of pseudorange corrections. For example, ionospheric storm-enhanced plasma density (SED) events can cause the corrections to have large spatial variation, making them poor choices even for users close to a beacon. Earlier work in the area of DGPS beacon selection has identified several options including choosing the beacon closest to the user or the beacon with the least skywave interference. There have also been suggestions on how to combine corrections when multiple beacons are available. The most common of these is a weighted sum of the corrections, where the weights are typically inversely proportional to the distance from the user to the individual beacon. This paper reexamines the concept of multi-beacon DGPS by evaluating methods of combining beacon corrections based on spatial relativity. Of relevance to this topic is our recent observation that DGPS accuracy performance is biased. The mean of the error scatter with DGPS corrections does not fall on the actual receiver position. We established this both by processing GPS L1 C/A observables from hundreds of CORS (Continuously Operating References Station) sites around the U.S.A. and via simulation using a Spirent GSS8000 GPS simulator. Specifically, we found that the position solution computed using DGPS beacon corrections is typically biased in a direction away from the beacon, and that the size of the bias depends upon the distance from the beacon. This bias grows with a slope of approximately one-third of a meter per 100 km of user-to-beacon distance. This paper compares the performance of several multibeacon algorithms assessed using GPS simulator data. These algorithms include the nearest beacon, a weighted sum based on distances, and a spatial linearly-interpolated correction using the actual locations of the transmitters (distance and angle). We note that as part of this research effort we developed a DGPS receiver using software-defined radio (USRP). A complete description of this system is included in the paper

Cryogenic sapphire oscillator with exceptionally high long-term frequency stability

We report on the development of a sapphire cryogenic microwave resonator oscillator long-term fractional frequency stability of 2x10^-17Sqrt[\tau] for integration times \tau>10^3 s and negative drift of about 2.2x10^-15/day. The short-term frequency instability of the oscillator is highly reproducible and also state-of-the-art: 5.6x10^-16 for an integration time of \tau ~ 20 s.Comment: Accepted for publication in Applied Physics Letter

Ultra-Low Noise Microwave Extraction from Fiber-Based Optical Frequency Comb

In this letter, we report on all-optical fiber approach to the generation of ultra-low noise microwave signals. We make use of two erbium fiber mode-locked lasers phase locked to a common ultra-stable laser source to generate an 11.55 GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz from the carrier.The residual frequency instability of the microwave signals derived from the two optical frequency combs is below 2.3 10^(-16) at 1s and about 4 10^(-19) at 6.5 10^(4)s (in 5 Hz bandwidth, three days continuous operation).Comment: 12 pages, 3 figure

Recognising Desire: A psychosocial approach to understanding education policy implementation and effect

It is argued that in order to understand the ways in which teachers experience their work - including the idiosyncratic ways in which they respond to and implement mandated education policy - it is necessary to take account both of sociological and of psychological issues. The paper draws on original research with practising and beginning teachers, and on theories of social and psychic induction, to illustrate the potential benefits of this bipartisan approach for both teachers and researchers. Recognising the significance of (but somewhat arbitrary distinction between) structure and agency in teachers’ practical and ideological positionings, it is suggested that teachers’ responses to local and central policy changes are governed by a mix of pragmatism, social determinism and often hidden desires. It is the often underacknowledged strength of desire that may tip teachers into accepting and implementing policies with which they are not ideologically comfortable

Characterization of Retinal Structure in ATF6-Associated Achromatopsia.

PurposeMutations in six genes have been associated with achromatopsia (ACHM): CNGA3, CNGB3, PDE6H, PDE6C, GNAT2, and ATF6. ATF6 is the most recent gene to be identified, though thorough phenotyping of this genetic subtype is lacking. Here, we sought to test the hypothesis that ATF6-associated ACHM is a structurally distinct form of congenital ACHM.MethodsSeven genetically confirmed subjects from five nonconsanguineous families were recruited. Foveal hypoplasia and the integrity of the ellipsoid zone (EZ) band (a.k.a., IS/OS) were graded from optical coherence tomography (OCT) images. Images of the photoreceptor mosaic were acquired using confocal and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). Parafoveal cone and rod density values were calculated and compared to published normative data as well as data from two subjects harboring CNGA3 or CNGB3 mutations who were recruited for comparative purposes. Additionally, nonconfocal dark-field AOSLO images of the retinal pigment epithelium were obtained, with quantitative analysis performed in one subject with ATF6-ACHM.ResultsFoveal hypoplasia was observed in all subjects with ATF6 mutations. Absence of the EZ band within the foveal region (grade 3) or appearance of a hyporeflective zone (grade 4) was seen in all subjects with ATF6 using OCT. There was no evidence of remnant foveal cone structure using confocal AOSLO, although sporadic cone-like structures were seen in nonconfocal split-detection AOSLO. There was a lack of cone structure in the parafovea, in direct contrast to previous reports.ConclusionsOur data demonstrate a near absence of cone structure in subjects harboring ATF6 mutations. This implicates ATF6 as having a major role in cone development and suggests that at least a subset of subjects with ATF6-ACHM have markedly fewer cellular targets for cone-directed gene therapies than do subjects with CNGA3- or CNGB3-ACHM