Impact of surface-polish on the angular and wavelength dependence of fiber focal ratio degradation

We present measurements of how multimode fiber focal-ratio degradation (FRD) and throughput vary with levels of fiber surface polish from 60 to 0.5 micron grit. Measurements used full-beam and laser injection methods at wavelengths between 0.4 and 0.8 microns on 17 meter lengths of Polymicro FBP 300 and 400 micron core fiber. Full-beam injection probed input focal-ratios between f/3 and f/13.5, while laser injection allowed us to isolate FRD at discrete injection angles up to 17 degrees (f/1.6 marginal ray). We find (1) FRD effects decrease as grit size decreases, with the largest gains in beam quality occurring at grit sizes above 5 microns; (2) total throughput increases as grit size decreases, reaching 90% at 790 nm with the finest polishing levels; (3) total throughput is higher at redder wavelengths for coarser polishing grit, indicating surface-scattering as the primary source of loss. We also quantify the angular dependence of FRD as a function of polishing level. Our results indicate that a commonly adopted micro-bending model for FRD is a poor descriptor of the observed phenomenon.Comment: 10 pages, 7 figures, presented at SPIE Astronomical Telescopes and Instrumentation, July 201

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis.

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.R01 GM073855 - NIGMS NIH HHS; R01 GM096129 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HH

Charter School Funding: Inequity in the City

Public charter schools are a growing part of K-12 education. Charter schools are public schools that are granted operational autonomy by their authorizing agency in return for a commitment to achieve specific performance goals. Like traditional public schools, charter schools are free to students and overseen by the state. Unlike traditional public schools, however, most charters are open to all students who wish to apply, regardless of where they live. If a charter school is over-subscribed, usually random lotteries determine which students will be admitted. Most charter schools are independent of the traditional public school district in which they operate

Measurements of the Yield Stress in Frictionless Granular Systems

We perform extensive molecular dynamics simulations of 2D frictionless granular materials to determine whether these systems can be characterized by a single static yield shear stress. We consider boundary-driven planar shear at constant volume and either constant shear force or constant shear velocity. Under steady flow conditions, these two ensembles give similar results for the average shear stress versus shear velocity. However, near jamming it is possible that the shear stress required to initiate shear flow can differ substantially from the shear stress required to maintain flow. We perform several measurements of the shear stress near the initiation and cessation of flow. At fixed shear velocity, we measure the average shear stress $\Sigma_{yv}$ in the limit of zero shear velocity. At fixed shear force, we measure the minimum shear stress $\Sigma_{yf}$ required to maintain steady flow at long times. We find that in finite-size systems $\Sigma_{yf} > \Sigma_{yv}$, which implies that there is a jump discontinuity in the shear velocity from zero to a finite value when these systems begin flowing at constant shear force. However, our simulations show that the difference $\Sigma_{yf} - \Sigma_{yv}$, and thus the discontinuity in the shear velocity, tend to zero in the infinite system size limit. Thus, our results indicate that in the large system limit, frictionless granular systems are characterized by a single static yield shear stress. We also monitor the short-time response of these systems to applied shear and show that the packing fraction of the system and shape of the velocity profile can strongly influence whether or not the shear stress at short times overshoots the long-time average value.Comment: 7 pages and 6 figure

The calcium current in inner segments of rods from the salamander (Ambystoma tigrinum) retina.

Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole-cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e. tetraethylammonium as a cation, and aspartate or methanesulphonate as an anion), an inward current remained. It activated at approximately -40 mV, reached a maximum at approximately 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half-maximum shifted from approximately -22 to -31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both time constants for deactivation were independent of voltage (between -30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM-EGTA, the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes

Herbicide Control of Broom Snakeweed (Gutierrezia sarothrae)

Broom snakeweed (Gutierrezia sarothrae [Pursh] Britton & Rusby) is a native invasive species that is widely distributed across western North America. It is very competitive with other vegetation and can reduce or displace desirable grasses and forbs. Removal of snakeweed from rangelands can result in increased forage production of desirable plant species. The evaluation of new herbicides to determine their efficacy in controlling broom snakeweed assists in providing land managers with alternatives to control broom snakeweed. The objective of this study was to evaluate herbicides applied in the spring to determine efficacy of control of broom snakeweed. 2,4-D + triclopyr had the greatest reduction in snakeweed density at 97 ± 14.6 % (P \u3c 0.0001). Aminopyralid and 2,4-D were also effective at reducing snakeweed density at 73 ± 14.6 % control. Our results demonstrate that 2,4-D + triclopyr, a new herbicide, can be used in controlling broom snakeweed in the spring

HexPak and GradPak: variable-pitch dual-head IFUs for the WIYN 3.5m Telescope Bench Spectrograph

We describe the design, construction, and expected performance of two new fiber integral field units (IFUs) --- HexPak and GradPak --- for the WIYN 3.5m Telescope Nasmyth focus and Bench Spectrograph. These are the first IFUs to provide formatted fiber integral field spectroscopy with simultaneous sampling of varying angular scales. HexPak and GradPak are in a single cable with a dual-head design, permitting easy switching between the two different IFU heads on the telescope without changing the spectrograph feed: the two heads feed a variable-width double-slit. Each IFU head is comprised of a fixed arrangement of fibers with a range of fiber diameters. The layout and diameters of the fibers within each array are scientifically-driven for observations of galaxies: HexPak is designed to observe face-on spiral or spheroidal galaxies while GradPak is optimized for edge-on studies of galaxy disks. HexPak is a hexagonal array of 2.9 arcsec fibers subtending a 40.9 arcsec diameter, with a high-resolution circular core of 0.94 arcsec fibers subtending 6 arcsec diameter. GradPak is a 39 by 55 arcsec rectangular array with rows of fibers of increasing diameter from angular scales of 1.9 arcsec to 5.6 arcsec across the array. The variable pitch of these IFU heads allows for adequate sampling of light profile gradients while maintaining the photon limit at different scales.Comment: 10 pages, 4 figures, presented at SPIE, Astronomical Telescopes and Instrumentation, 1 - 6 July 2012, Amsterdam, Netherland

Organization of GC/MS and LC/MS metabolomics data into chemical libraries

<p>Abstract</p> <p>Background</p> <p>Metabolomics experiments involve generating and comparing small molecule (metabolite) profiles from complex mixture samples to identify those metabolites that are modulated in altered states (e.g., disease, drug treatment, toxin exposure). One non-targeted metabolomics approach attempts to identify and interrogate all small molecules in a sample using GC or LC separation followed by MS or MSⁿdetection. Analysis of the resulting large, multifaceted data sets to rapidly and accurately identify the metabolites is a challenging task that relies on the availability of chemical libraries of metabolite spectral signatures. A method for analyzing spectrometry data to identify and <b>Qu</b>antify <b>I</b>ndividual <b>C</b>omponents in a <b>S</b>ample, (QUICS), enables generation of chemical library entries from known standards and, importantly, from unknown metabolites present in experimental samples but without a corresponding library entry. This method accounts for all ions in a sample spectrum, performs library matches, and allows review of the data to quality check library entries. The QUICS method identifies ions related to any given metabolite by correlating ion data across the complete set of experimental samples, thus revealing subtle spectral trends that may not be evident when viewing individual samples and are likely to be indicative of the presence of one or more otherwise obscured metabolites.</p> <p>Results</p> <p>LC-MS/MS or GC-MS data from 33 liver samples were analyzed simultaneously which exploited the inherent biological diversity of the samples and the largely non-covariant chemical nature of the metabolites when viewed over multiple samples. Ions were partitioned by both retention time (RT) and covariance which grouped ions from a single common underlying metabolite. This approach benefitted from using mass, time and intensity data in aggregate over the entire sample set to reject outliers and noise thereby producing higher quality chemical identities. The aggregated data was matched to reference chemical libraries to aid in identifying the ion set as a known metabolite or as a new unknown biochemical to be added to the library.</p> <p>Conclusion</p> <p>The QUICS methodology enabled rapid, in-depth evaluation of all possible metabolites (known and unknown) within a set of samples to identify the metabolites and, for those that did not have an entry in the reference library, to create a library entry to identify that metabolite in future studies.</p

FDA Food Code recommendations: how do popular US baking shows measure up?

The purpose of this study was to determine if popular US baking shows follow the FDA Food Code recommendations and critical food safety principles. This cross-sectional study examined a convenience sample of 75 episodes from three popular baking shows. The three shows were about competitively baking cupcakes, competitively baking cakes, and baking in a popular local bakery. Twenty-five episodes from each show were viewed. Coding involved tallying how many times 17 FDA Food Code recommendations were or were not followed. On each show, bare hands frequently came in contact with ready-to-eat food. On a per-hour basis, this occurred 80, 155, and 176 times on shows 1-3, respectively. Hands were washed before cooking three times on the three shows and never for the recommended 20 seconds. On each show, many people touched food while wearing jewelry other than a plain wedding band, for an average of at least 7 people per hour on each show. Shows 1-3 had high rates of long-haired bakers not wearing hair restraints (11.14, 6.57, and 14.06 per hour, respectively). Shows 1 and 2 had high rates of running among the bakers (22.29 and 10.57 instances per hour, respectively). These popular baking shows do not demonstrate proper food safety techniques put forth by the FDA and do not contribute the reduction of foodborne illnesses through proper food handling