Designs and Optical Tests of Thermal Links for an Optical Refrigerator

Dielectric mirror leakage at large angles of incidence limits the effectiveness of solid state optical refrigerators due to reheating caused by photon absorption in an attached load. In this paper, we present several thermally conductive link solutions to greatly reduce the net photon absorption. The Los Alamos Solid State Optical Refrigerator (LASSOR) has demonstrated cooling of a Yb/sup 3+/ doped ZBLANP glass to 208 K. We have designed optically isolating thermal link geometries capable of extending cooling to a typical heat load with minimal absorptive reheating, and we have tested the optical performance of these designs. A surrogate source operating at 625 nm was used to mimic the angular distribution of light from the LASSOR cooling element. While total link performance is dependent on additional factors, we have found that the best thermal link reduced the net transmission of photons to 0.04%, which includes the trapping mirrors 8.1% transmission. Our measurements of the optical performance of the various link geometries are supported by computer simulations of the designs using Code V, a commercially available optical modeling software package

Computer Modeling and Analysis of Thermal Link Performance for an Optical Refrigerator

We have used the thermal modeling tool in COMSOL Multiphysics to investigate factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a non-absorptive dielectric trapping mirror, the three dominant heating factors are blackbody radiation from the surrounding environment, conductive heat transfer through mechanical supports, and the absorption of fluorescent photons transmitted through the thermal link. Laboratory experimentation coupled with computer modeling using Code V optical software have resulted in link designs capable of reducing the transmission to 0.04% of the fluoresced photons emitted toward the thermal link. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. Modeling results imply that a 1 cm/sup 3/ load can be chilled to 102 K with currently available cooling efficiencies using a 100 W pump laser on a YB:ZBLANP system, and using an ideal link that has minimal surface area and no optical transmission. We review the simulated steady-state cooling temperatures reached by the heat load for several link designs and system configurations as a comparative measure of how well particular configurations perform

Thermal Links for the Implementation of an Optical Refrigerator

Optical refrigeration has been demonstrated by several groups of researchers, but the cooling elements have not been thermally linked to realistic heat loads in ways that achieve the desired temperatures. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. We have designed thermal links that minimize the absorption of fluoresced photons by the heat load using multiple mirrors and geometric shapes including a hemisphere, a kinked waveguide, and a tapered waveguide. While total link performance is dependent on additional factors, we have observed net transmission of photons with the tapered link as low as 0.04%. Our optical tests have been performed with a surrogate source that operates at 625 nm and mimics the angular distribution of light emitted from the cooling element of the Los Alamos solid state optical refrigerator. We have confirmed the optical performance of our various link geometries with computer simulations using CODE V optical modeling software. In addition we have used the thermal modeling tool in COMSOL MULTIPHYSICS to investigate other heating factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a nonabsorptive dielectric trapping mirror, the three dominant heating factors are (1) absorption of fluoresced photons transmitted through the thermal link, (2) blackbody radiation from the surrounding environment, and (3) conductive heat transfer through mechanical supports. Modeling results show that a 1 cm3 load can be chilled to 107 K with a 100Wpump laser. We have used the simulated steady-state cooling temperatures of the heat load to compare link designs and system configurations

The critical role of the linear plasmid lp36 in the infectious cycle of Borrelia burgdorferi

Borrelia burgdorferi, the aetiological agent of Lyme disease, follows a life cycle that involves passage between the tick vector and the mammalian host. To investigate the role of the 36 kb linear plasmid, lp36 (also designated the B. burgdorferi K plasmid), in the infectious cycle of B. burgdorferi, we examined a clone lacking this plasmid, but containing all other plasmids known to be required for infectivity. Our results indicated that lp36 was not required for spirochete survival in the tick, but the clone lacking lp36 demonstrated low infectivity in the mammal. Restoration of lp36 to the mutant strain confirmed that the infectivity defect was due to loss of lp36. Moreover, spirochetes lacking lp36 exhibited a nearly 4-log increase in ID50 relative to the isogenic lp36+ clone. The infectivity defect of lp36-minus spirochetes was localized, in part, to loss of the bbk17 (adeC) gene, which encodes an adenine deaminase. This work establishes a vital role for lp36 in the infectious cycle of B. burgdorferi and identifies the bbk17 gene as a component of this plasmid that contributes to mammalian infectivity

Recommendations for early referral of individuals with suspected polymyalgia rheumatica: An initiative from the international giant cell arteritis and polymyalgia rheumatica study group

Objective To develop international consensus-based recommendations for early referral of individuals with suspected polymyalgia rheumatica (PMR). Methods A task force including 29 rheumatologists/ internists, 4 general practitioners, 4 patients and a healthcare professional emerged from the international giant cell arteritis and PMR study group. The task force supplied clinical questions, subsequently transformed into Population, Intervention, Comparator, Outcome format. A systematic literature review was conducted followed by online meetings to formulate and vote on final recommendations. Levels of evidence (LOE) (1–5 scale) and agreement (LOA) (0–10 scale) were evaluated. Results Two overarching principles and five recommendations were developed. LOE was 4–5 and LOA ranged between 8.5 and 9.7. The recommendations suggest that (1) each individual with suspected or recently diagnosed PMR should be considered for specialist evaluation, (2) before referring an individual with suspected PMR to specialist care, a thorough history and clinical examination should be performed and preferably complemented with urgent basic laboratory investigations, (3) individuals with suspected PMR with severe symptoms should be referred for specialist evaluation using rapid access strategies, (4) in individuals with suspected PMR who are referred via rapid access, the commencement of glucocorticoid therapy should be deferred until after specialist evaluation and (5) individuals diagnosed with PMR in specialist care with a good initial response to glucocorticoids and a low risk of glucocorticoid related adverse events can be managed in primary care. Conclusions These are the first international recommendations for referral of individuals with suspected PMR, which complement the European Alliance of Associations for Rheumatology/American College of Rheumatology management guidelines for established PMR

Application of Model-Based Systems Engineering (MBSE) to compare legacy and future forces in Mine Warfare (MIW) missions

This capstone report describes the expected mine countermeasures (MCM) performance of the Avenger class MCM ship (MCM 1), landing helicopter deck (LHD) support ship, and MH-53E helicopter legacy systems and Increment 1 of the littoral combat ship (LCS) and MH-60S helicopter future systems. The study focused on two measures of effec-tiveness (MOEs): area coverage rate sustained (ACRS) and percent clearance of mines. The systems engineering (SE) approach used to address stakeholder needs identified foundational requirements and developed functional and physi-cal architectures for simulation in conducting the comparative technical analysis. A design of experiments (DOE) methodology was used to determine which factors have the greatest influence on the MOEs. The significant factors’ values were varied to develop a set of recommended improvements to the future MCM systems. The study found that maintaining a constant search speed of 10 knots, improving the stream and recover time to 15 minutes, and improving the sortie time to 24 hours for the remote minehunting system (RMS) would provide a future ACRS performance greater than that provided by the legacy systems. When factoring in risk and operating and sustainment (O&S) costs, the future capability and recommended improvements provide better performance per cost than the legacy capability.http://archive.org/details/applicationofmod1094544659Approved for public release; distribution is unlimited

GuaA and GuaB Are Essential for Borrelia burgdorferi Survival in the Tick-Mouse Infection Cycle▿

Pathogens lacking the enzymatic pathways for de novo purine biosynthesis are required to salvage purines and pyrimidines from the host environment for synthesis of DNA and RNA. Two key enzymes in purine salvage pathways are IMP dehydrogenase (GuaB) and GMP synthase (GuaA), encoded by the guaB and guaA genes, respectively. While these genes are typically found on the chromosome in most bacterial pathogens, the guaAB operon of Borrelia burgdorferi is present on plasmid cp26, which also harbors a number of genes critical for B. burgdorferi viability. Using molecular genetics and an experimental model of the tick-mouse infection cycle, we demonstrate that the enzymatic activities encoded by the guaAB operon are essential for B. burgdorferi mouse infectivity and provide a growth advantage to spirochetes in the tick. These data indicate that the GuaA and GuaB proteins are critical for the survival of B. burgdorferi in the infection cycle and highlight a potential difference in the requirements for purine salvage in the disparate mammalian and tick environments

Restoration of W1282X CFTR Activity by Enhanced Expression

Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Premature termination codons represent a common minority of CFTR mutations, and are caused by base pair substitutions that produce abnormal stop codons in the coding sequence. Select aminoglycosides induce “translational readthrough” of premature stop codons and have been shown to restore full-length functional protein in a number of preclinical and clinical settings. We studied two well-described premature termination codons found in the distal open reading frame of CFTR, W1282X and R1162X, expressed in polarizing and nonpolarizing cells. Our findings indicate that W1282X CFTR–expressing cells demonstrate significantly greater CFTR activity when overexpressed compared with R1162X CFTR cells, even when truncated protein is the predominant form. In addition, our results show that the combination of stimulated expression and stop codon suppression produces additive effects on CFTR-mediated ion transport. These findings provide evidence that W1282X CFTR exhibits membrane localization and retained chloride channel function after enhanced expression, and suggest that patients harboring this mutation may be more susceptible to CFTR rescue