A unified model for multi-turn closed-loop pulsating heat pipe

Numerical modeling of  the multi-turn closed-loop pulsating heat pipe (CLPHP) in the bottom, horizontal, and top heat mode is presented in this paper, with water as working fluid. Modeling is carried out for 2-mm ID CLPHP having 5, 16, and 32 turns at different orientations for 10 different cases. Momentum and heat transfer variations with time are investigated by numerically solving the one-dimensional governing equations for vapor bubble and liquid plugs. Instead of considering all the vapor bubble at saturation temperature, vapor bubbles are allowed to remain in super-heated condition. Film thickness is found using a correlation. Two-phase heat transfer coefficient is calculated by considering conduction through the thin film at liquid–vapor interface. Liquid plug merging and splitting result in continuous variation in the number of liquid plugs and vapor bubble with time, which is also considered in the code. During the merging of liquid plugs, a time step-adaptive scheme is implemented and this minimum time step was found to be 10⁻⁷ s. Model results are compared with the experimental results from literature for heat transfer and the maximum variation in heat transfer for all these cases is below ±39%.     

Full-field phase modulation characterization of liquid-crystal spatial light modulator using digital holography

A direct quantitative phase measurement method to characterize intrinsic phase modulation from an entire active area of transmissive twisted-nematic liquid-crystal spatial light modulator (TN-LCSLM) is presented using digital holography (DH). The change in birefringence of liquid crystal material with respect to addressed gray scale produces phase modulation of wavefront transmitted through TN-LCSLM. Existing methods for phase modulation characterization of LCSLM mainly provides point measurement on its total active region. In this paper, the DH method is evolved to extract quantitative phase information of an entire active area from a single digital hologram formed using the complex wavefront transmitted through TN-LCSLM.     

Physical and chemical analyses of pigeonpea (Cajanus cajan) cultivars and F1 crosses

The weight of ‘dhal’ (the edible part of the seed) from 100 whole seeds, and the hull, protein, fat, starch and soluble carbohydrate contents of 12 pigeonpea (Cajanus cajan) cultivars and the F₁ crosses were determined. The mean values for cultivars and the F₁ crosses differed in 100-seed wt, hull content (%) and protein and starch contents. Whereas 100-seed wt showed a high positive correlation with the weight of dhal, its correlation was significantly negative with hull content (%) in cultivars and protein content in the F₁ crosses.     

Size-fractionated measurements of ambient ultrafine particle chemical composition in Los Angeles using the NanoMOUDI

Ambient ultrafine particles have gained attention with recent evidence showing them to be more toxic than larger ambient particles. Few studies have investigated the distribution of chemical constituents within the ultrafine range. The current study explores the size-fractionated ultrafine (10-180 nm) chemical composition at urban source sites (USC and Long Beach) and inland receptor sites (Riverside and Upland) in the Los Angeles basin over three different seasons. Size-fractionated ultrafine particles were collected by a NanoMOUDI over a period of 2 weeks at each site. Measurements of ultrafine mass concentrations varied from 0.86 to 3.5 microg/m3 with the highest concentrations observed in the fall. The chemical composition of ultrafine particles ranged from 32 to 69% for organic carbon (OC), 1-34% for elemental carbon (EC), 0-24% for sulfate, and 0-4% for nitrate. A distinct OC mode was observed between 18 and 56 nm in the summer, possibly indicating photochemical secondary organic aerosol formation. The EC levels are higher in winter at the source sites due to lower inversion heights and are higher in summer at the receptor sites due to increased long-range transport from upwind source areas. Nitrate and sulfate were measurable only in the larger particle size ranges of ultrafine PM. Collocated continuous measurements of particle size distributions and gaseous pollutants helped to differentiate ultrafine particle sources at each site.     

New approaches toward recognition of nucleic acid triple helices

A DNA duplex can be recognized sequence-specifically in the major groove by an oligodeoxynucleotide (ODN). The resulting structure is a DNA triple helix, or triplex. The scientific community has invested significant research capital in the study of DNA triplexes because of their robust potential for providing new applications, including molecular biology tools and therapeutic agents. The triplex structures have inherent instabilities, however, and the recognition of DNA triplexes by small molecules has been attempted as a means of strengthening the three-stranded complex. Over the decades, the majority of work in the field has focused on heterocycles that intercalate between the triplex bases. In this Account, we present an alternate approach to recognition and stabilization of DNA triplexes. We show that groove recognition of nucleic acid triple helices can be achieved with aminosugars. Among these aminosugars, neomycin is the most effective aminoglycoside (groove binder) for stabilizing a DNA triple helix. It stabilizes both the TAT triplex and mixed-base DNA triplexes better than known DNA minor groove binders (which usually destabilize the triplex) and polyamines. Neomycin selectively stabilizes the triplex (TAT and mixed base) without any effect on the DNA duplex. The selectivity of neomycin likely originates from its potential and shape complementarity to the triplex Watson-Hoogsteen groove, making it the first molecule that selectively recognizes a triplex groove over a duplex groove. The groove recognition of aminoglycosides is not limited to DNA triplexes, but also extends to RNA and hybrid triple helical structures. Intercalator-neomycin conjugates are shown to simultaneously probe the base stacking and groove surface in the DNA triplex. Calorimetric and spectrosocopic studies allow the quantification of the effect of surface area of the intercalating moiety on binding to the triplex. These studies outline a novel approach to the recognition of DNA triplexes that incorporates the use of noncompeting binding sites. These principles of dual recognition should be applicable to the design of ligands that can bind any given nucleic acid target with nanomolar affinities and with high selectivity.     

Comparative Study of the Leak Characteristics of Two Ceramic/Glass Composite Seals for Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have the potential to play a significant role in a future clean energy economy. However, SOFCs still face major obstacles before they can be commercialized, with efficient sealing being among the most prominent. The present research focuses on the comparative study of microstructure, crystal phase evolution, and leak rates, for two ceramic/glass seals used in an SOFC. The leak test apparatus is a controlled facility designed to incorporate different mechanical loading, stack configurations, and thermal cycles. Simultaneous leak testing with an acoustic emission (AE) sensor was also used to identify any micro‐damage in seals. A two‐level factorial design was applied to the first sealing composition to identify the main and the interactive factors for leak rates. MINITAB^® was also used to determine a linear regression‐based leak rate model. The second seal formulation employed a more stable glass which led to reduced leak rates. Additional factors in a two‐level factorial design were investigated for the second seal formulation. Based on multiple experiments with different stack components, it was determined that the number of interfaces is most critical for leak rate, showing that even in the presence of thermal cycling, leakage is an interfacial dominated phenomenon.     

Light Extraction Efficiency Enhancement of Colloidal Quantum Dot Light‐Emitting Diodes Using Large‐Scale Nanopillar Arrays

A colloidal quantum dot light‐emitting diode (QLED) is reported with substantially enhanced light extraction efficiency by applying a layer of large‐scale, low‐cost, periodic nanopillar arrays. Zinc oxide nanopillars are grown on the glass surface of the substrate using a simple, efficient method of non‐wetting templates. With the layer of ZnO nanopillar array as an optical outcoupling medium, a record high current efficiency (CE) of 26.6 cd/A is achieved for QLEDs. Consequently, the corresponding external quantum efficiency (EQE) of 9.34% reaches the highest EQE value for green‐emitting QLEDs. Also, the underlying physical mechanisms enabling the enhanced light‐extraction are investigated, which leads to an excellent agreement of the numerical results based on the mode theory with the experimental measurements. This study is the first account for QLEDs offering detailed insight into the light extraction efficiency enhancement of QLED devices. The method demonstrated here is intended to be useful not only for opening up a ubiquitous strategy for designing high‐performance QLEDs but also with respect to fundamental research on the light extraction in QLEDs.     

Visual outcomes following lensectomy and vitrectomy for combined anterior and posterior persistent hyperplastic primary vitreous

OBJECTIVE: To determine the visual outcome after surgery for persistent hyperplastic primary vitreous using modern vitreoretinal techniques. DESIGN: Retrospective medical record review during a 5-year period (June 1992 to June 1997). Information recorded for each patient included age, medical history, sex, results of preoperative ocular examination, age at diagnosis, procedure performed, intraoperative and postoperative complications, location and number of sclerotomy sites, type of aphakic rehabilitation, amblyopic therapy given, final visual acuity, and length of follow-up. RESULTS: Fourteen patients who underwent surgical management of combined anterior and posterior persistent hyperplastic primary vitreous were identified. Eleven patients underwent aphakic rehabilitation and aggressive amblyopic therapy consisting of occlusive therapy for several waking hours each day. One additional older patient received aphakic rehabilitation only. Ten eyes (71%) achieved a visual acuity of 20/300 or better, and 8 (57%) obtained a final visual acuity of 20/100 or better. Average length of follow-up was 22 months (range, 4-57 months). Nine patients were fitted with an aphakic soft contact lens, 2 older patients had a posterior chamber intraocular lens placed at the time of vitrectomy, and 1 patient wore aphakic spectacles. CONCLUSIONS: With modern vitreoretinal techniques, aphakic rehabilitation, and aggressive amblyopic therapy, useful vision can be obtained in the majority of patients with combined anterior and posterior persistent hyperplastic primary vitreous.