On the Aggregation of Inertial Particles in Random Flows

We describe a criterion for particles suspended in a randomly moving fluid to aggregate. Aggregation occurs when the expectation value of a random variable is negative. This random variable evolves under a stochastic differential equation. We analyse this equation in detail in the limit where the correlation time of the velocity field of the fluid is very short, such that the stochastic differential equation is a Langevin equation.Comment: 16 pages, 2 figure

Optimal focusing for maximal collection of entangled narrow-band photon pairs into single-mode fibers

We present a theoretical and experimental investigation of the emission characteristics and the flux of photon pairs generated by spontaneous parametric downconversion in quasi-phase matched bulk crystals for the use in quantum communication sources. We show that, by careful design, one can attain well defined modes close to the fundamental mode of optical fibers and obtain high coupling efficiencies also for bulk crystals, these being more easily aligned than crystal waveguides. We distinguish between singles coupling, conditional coincidence, and pair coupling, and show how each of these parameters can be maximized by varying the focusing of the pump mode and the fiber-matched modes using standard optical elements. Specifically we analyze a periodically poled KTP-crystal pumped by a 532 nm laser creating photon pairs at 810 nm and 1550 nm. Numerical calculations lead to coupling efficiencies above 94% at optimal focusing, which is found by the geometrical relation L/z_R to be ~ 1 to 2 for the pump mode and ~ 2 to 3 for the fiber-modes, where L is the crystal length and z_R is the Rayleigh-range of the mode-profile. These results are independent on L. By showing that the single-mode bandwidth decreases as 1/L, we can therefore design the source to produce and couple narrow bandwidth photon pairs well into the fibers. Smaller bandwidth means both less chromatic dispersion for long propagation distances in fibers, and that telecom Bragg gratings can be utilized to compensate for broadened photon packets--a vital problem for time-multiplexed qubits. Longer crystals also yield an increase in fiber photon flux proportional to sqrt{L}, and so, assuming correct focusing, we can only see advantages using long crystals.Comment: 19 pages, 15 figures, ReVTeX4, minor revisio

How product characteristics can guide measures for resource efficiency - A synthesis of assessment studies

A circular economy aims at decoupling value creation from resource throughput. For circular economy to contribute to environmental and resource improvements, there is need for critical assessments regarding in what general situations, beyond individual cases, solutions may lead to improvements. On the product-level, there is need for synthesized knowledge accounting for a wide range of contexts and environmental impacts. We investigate what resource efficiency (RE) measures result in reduced physical flows and environmental impacts, depending on the characteristics of products and their life cycles. The study is limited to physical measures on a product system level, irrespective of manner of implementation. A library of comparative assessments (primarily life cycle assessments and material flow analyses) was built, covering a wide range of products and RE measures. A framework was formulated for analysing for which product characteristics a measure tends to improve RE, and under which contexts there are trade-offs to take into account. For example, sharing of products is best suited for durable and infrequently used products that tend not to reach their full technical lifetime. A trade-off is that sharing can increase transportation for accessing shared stock. The identified key product characteristics were: whether products are consumable or durable, active or passive, typically used for their full technical lifetimes or discarded before being worn out, the product’s frequency of use and whether function remains at a product’s end of use. Pace of development matters for suitability of measures for active, durable products, while complexity is relevant for restorative measures and recycling

Highly Efficient Source for Indistinguishable Photons of Controlled Shape

We demonstrate a straightforward implementation of a push-button like single-photon source which is based on a strongly coupled atom-cavity system. The device operates intermittently for periods of up to 100 microseconds, with single-photon repetition rates of 1.0 MHz and an efficiency of 60 %. Atoms are loaded into the cavity using an atomic fountain, with the upper turning point near the cavity's mode centre. This ensures long interaction times without any disturbances induced by trapping potentials. The latter is the key to reaching deterministic efficiencies as high as obtained in probabalistic photon-heralding schemes. The price to pay is the random loading of atoms into the cavity and the resulting intermittency. However, for all practical purposes, this has a negligible impact

Regulation of CD1 Antigen-presenting Complex Stability

For major histocompatibility complex class I and II molecules, the binding of specific peptide antigens is essential for assembly and trafficking and is at the center of their quality control mechanism. However, the role of lipid antigen binding in stabilization and quality control of CD1 heavy chain (HC).beta(2)-microglobulin (beta(2)m) complexes is unclear. Furthermore, the distinct trafficking and loading routes of CD1 proteins take them from mildly acidic pH in early endososmal compartments (pH 6.0) to markedly acidic pH in lysosomes (pH 5.0) and back to neutral pH of the cell surface (pH 7.4). Here, we present evidence that the stability of each CD1 HC.beta(2)m complex is determined by the distinct pH optima identical to that of the intracellular compartments in which each CD1 isoform resides. Although stable at acidic endosomal pH, complexes are only stable at cell surface pH 7.4 when bound to specific lipid antigens. The proposed model outlines a quality control program that allows lipid exchange at low endosomal pH without dissociation of the CD1 HC.beta(2)m complex and then stabilizes the antigen-loaded complex at neutral pH at the cell surface

The taste for the particular: A logic of discernment in an age of omnivorousness

This article provides an analysis of two leading specialist wine magazines, Decanter and Wine Spectator, and the codification and legitimation of a ‘taste for the particular.’ Such media of connoisseurship are key institutions of evaluation and legitimation in an age of omnivorousness, but are often overlooked in research that foregrounds the agency of tasters and neglects the conventionalization of tasting norms and devices. The wine field has undergone a process of democratization typical of omnivorousness more broadly: former elite/low boundaries (operationalized in the paper through the Old/New World dichotomy) are ignored, and a discerning attitude is encouraged for wines from a diversity of regions. Drawing on the magazines’ audience profile and market position data, and a content analysis of advertising and editorial content from 2008 and 2010, I examine the differences in the use of four legitimation frames (transparency, heritage, genuineness and external validation) for the provenance elements of Old and New World wines. The analysis suggests that the Old World—typically French—notion of terroir, on which the traditional Old/New World boundary rested, has been democratized through the particularities of provenance. Yet, the analysis also reveals continuing differences between the two categories (including greater emphasis on the heritage and external validation of Old World context of production, and on the transparency and genuineness of New World producers), and the preservation of established hierarchies of taste through the application of terroir to New World wines, which retain the Old World and France as their master referent

The Palomar Testbed Interferometer Calibrator Catalog

The Palomar Testbed Interferometer (PTI) archive of observations between 1998 and 2005 is examined for objects appropriate for calibration of optical long-baseline interferometer observations - stars that are predictably point-like and single. Approximately 1,400 nights of data on 1,800 objects were examined for this investigation. We compare those observations to an intensively studied object that is a suitable calibrator, HD217014, and statistically compare each candidate calibrator to that object by computing both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis is that the frequency distribution of visibility data associated with calibrator stars differs from non-calibrator stars such as binary stars. Spectroscopic binaries resolved by PTI, objects known to be unsuitable for calibrator use, are similarly tested to establish detection limits of this approach. From this investigation, we find more than 350 observed stars suitable for use as calibrators (with an additional $\approx 140$ being rejected), corresponding to $\gtrsim 95$ sky coverage for PTI. This approach is noteworthy in that it rigorously establishes calibration sources through a traceable, empirical methodology, leveraging the predictions of spectral energy distribution modeling but also verifying it with the rich body of PTI's on-sky observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n