Atom Interferometry with up to 24-Photon-Momentum-Transfer Beam Splitters

We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ-) and 144-fold for Ramsey-Borde (RB-) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel.Comment: New introduction. 4 pages, 4 figure

Extended cavity diode lasers with tracked resonances

We present a painless, almost-free upgrade to present extended cavity diode lasers (ECDLs), which improves the long term mode-hop free performance by stabilizing the resonance of the internal cavity to the external cavity. This stabilization is based on the observation that the frequency or amplitude noise of the ECDL is lowest at the optimum laser diode temperature or injection current. Thus, keeping the diode current at the level where the noise is lowest ensures mode-hop free operation within one of the stable regions of the mode chart, even if these should drift due to external influences. This method can be applied directly to existing laser systems without modifying the optical setup. We demonstrate the method in two ECDLs stabilized to vapor cells at 852 nm and 895 nm wavelength. We achieve long term mode-hop free operation and low noise at low power consumption, even with an inexpensive non-antireflection coated diode.Comment: 5 pages, 6 figure

Guest Editorial: Nonlinear Optimization of Communication Systems

Linear programming and other classical optimization techniques have found important applications in communication systems for many decades. Recently, there has been a surge in research activities that utilize the latest developments in nonlinear optimization to tackle a much wider scope of work in the analysis and design of communication systems. These activities involve every “layer” of the protocol stack and the principles of layered network architecture itself, and have made intellectual and practical impacts significantly beyond the established frameworks of optimization of communication systems in the early 1990s. These recent results are driven by new demands in the areas of communications and networking, as well as new tools emerging from optimization theory. Such tools include the powerful theories and highly efficient computational algorithms for nonlinear convex optimization, together with global solution methods and relaxation techniques for nonconvex optimization

Exotic Reservations – Low Price Guarantees

The increase in the volume of internet online bookings has had a major impact on distribution channels in the hotel industry. The popularity of such services stems from the consumers\u27 desire to obtain the lowest rate within their desired market segment. One possible cure is to offer the best rate guarantee. We show that current rate guarantees are essentially worthless to consumers; and demonstrate how a hotel company can structure a best rate guarantee that would provide value to consumers. In addition, we show, using a well-established exotic option pricing formula, how to price this best rate guarantee so that consumers would be willing to pay for the option

Multi-parameter Szemer\'{e}di-Trotter-type theorems and applications in finite fields

We prove some novel multi-parameter point-line incidence estimates in vector spaces over finite fields. While these could be seen as special cases of higher-dimensional incidence results, they outperform their more general counterparts in those contexts. We go on to present a number of applications to illustrate their use in combinatorial problems from geometry and number theory

Ethnic differences in the use of prescription drugs: a cross-sectional analysis of linked survey and administrative data

Background Evidence from the United States and Europe suggests that the use of prescription drugs may vary by ethnicity. In Canada, ethnic disparities in prescription drug use have not been as well documented as disparities in the use of medical and hospital care. We conducted a cross-sectional analysis of survey and administrative data to examine needs-adjusted rates of prescription drug use by people of different ethnic groups. Methods For 19 370 non-Aboriginal people living in urban areas of British Columbia, we linked data on self-identified ethnicity from the Canadian Community Health Survey with administrative data describing all filled prescriptions and use of medical services in 2005. We used sex-stratified multivariable logistic regression analysis to measure differences in the likelihood of filling prescriptions by drug class (antihypertensives, oral antibiotics, antidepressants, statins, respiratory drugs and nonsteroidal anti-inflammatory drugs [NSAIDs]). Models were adjusted for age, general health status, treatment-specific health status, socio-economic factors and recent immigration (within 10 years). Results We found evidence of significant needs-adjusted variation in prescription drug use by ethnicity. Compared with women and men who identified themselves as white, those who were South Asian or of mixed ethnicity were almost as likely to fill prescriptions for most types of medicines studied; moreover, South Asian men were more likely than white men to fill prescriptions for antibiotics and NSAIDs. The clearest pattern of use emerged among Chinese participants: Chinese women were significantly less likely to fill prescriptions for antihypertensives, antibiotics, antidepressants and respiratory drugs, and Chinese men for antidepressant drugs and statins. Interpretation We found some disparities in prescription drug use in the study population according to ethnic group. The nature of some of these variations suggest that ethnic differences in beliefs about pharmaceuticals may generate differences in prescription drug use; other variations suggest that there may be clinically important disparities in treatment use

Phase-Locked, Low-Noise, Frequency Agile Titanium: Sapphire Lasers for Simultaneous Atom Interferometers

We demonstrate phase lock of two >1.6W Titanium:sapphire lasers with a phase noise of -138dBc/Hz at 1MHz from the carrier, using an intra-cavity electro-optic phase modulator. The residual phase variance is 2.5 10^(-8)rad^2 integrated from 1Hz to 10kHz. Instantaneous offset frequency steps of up to 4MHz are achieved within 200ns. Simultaneous atom interferometers can make full use of this ultra-low phase noise in differential measurements by suppressing common influences from vibration of optics.Comment: Additional phase-noise data and references; to appear in Optics Letters. 3 pages, 4 figure

Performance-Based Optimization for Strut-Tie Modeling of Structural Concrete

Conventional trial-and-error methods are not efficient in developing appropriate strut-and-tie models in complex structural concrete members. This paper describes a performance-based optimization (PBO) technique for automatically producing optimal strut-and-tie models for the design and detailing of structural concrete. The PBO algorithm utilizes the finite element method as a modeling and analytical tool. Developing strut-and-tie models in structural concrete is treated as an optimal topology design problem of continuum structures. The optimal strut-and-tie model that idealizes the load transfer mechanism in cracked structural concrete is generated by gradually removing regions that are ineffective in carrying loads from a structural concrete member based on overall stiffness performance criteria. A performance index is derived for evaluating the performance of strut-and-tie systems in an optimization process. Fundamental concepts underlying the development of strut-and-tie models are introduced. Design examples of a low-rise concrete shearwall with openings and a bridge pier are presented to demonstrate the validity and effectiveness of the PBO technique as a rational and reliable design tool for structural concrete

Insect cryptochromes: gene duplication and loss define diverse ways to construct insect circadian clocks

Cryptochrome (CRY) proteins are components of the central circadian clockwork of metazoans. Phylogenetic analyses show at least 2 rounds of gene duplication at the base of the metazoan radiation, as well as several losses, gave rise to 2 cryptochrome (cry) gene families in insects, a Drosophila-like cry1 gene family and a vertebrate-like cry2 family. Previous studies have shown that insect CRY1 is photosensitive, whereas photo-insensitive CRY2 functions to potently inhibit clock-relevant CLOCK:CYCLE-mediated transcription. Here, we extended the transcriptional repressive function of insect CRY2 to 2 orders--Hymenoptera (the honeybee Apis mellifera and the bumblebee Bombus impatiens) and Coleoptera (the red flour beetle Tribolium castaneum). Importantly, the bee and beetle CRY2 proteins are not light sensitive in culture, in either degradation of protein levels or inhibitory transcriptional response, suggesting novel light input pathways into their circadian clocks as Apis and Tribolium do not have CRY1. By mapping the functional data onto a cryptochrome/6-4 photolyase gene tree, we find that the transcriptional repressive function of insect CRY2 descended from a light-sensitive photolyase-like ancestral gene, probably lacking the ability to repress CLOCK:CYCLE-mediated transcription. These data provide an evolutionary context for proposing novel circadian clock mechanisms in insects

Computing Energy Performance of Building Density, Shape and Typology in Urban Context

AbstractThis paper aims to better understand the impact of urban context on building energy consumption. The factors of external shading, shapes generated from zoning ordinances, and local climate are examined concerning three main questions: (1) how density influences building energy consumption generally, (2) how a given density generates alternative building shapes that have different impacts on energy performance, and (3) how different typologies affect the energy-density relationship. To answer them, a series of parametric simulation experiments are conducted based on Martin and March's urban block structure. For more than 14,000 hypothetical models located at the Portland urban grid, the energy consumptions for the purposes of cooling and heating are simulated using AutoCAD script, MATLAB and Energy Plus 8. The results suggest that, different from the common perceptions, building energy consumptions for cooling and heating purposes do not always have a negative relationship with density. Instead, the energy consumption has a negative relationship with density before a turning point, and then the relationship changes to be positive. Also with the same FAR, different building cover ratio and typologies can lead to large variations in energy consumption. By the experiments on different building shapes generated by urban frit, it was found that even with the same typology, the building energy consumption can still vary significantly. Finally, the exploration of climate factors indicates that in both Portland and Atlanta, the findings are similar except that the energy-density relationship is weaker in Atlanta than in Portland