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We have investigated the influence of the thickness of polyvinyl alcohol alignment layer on azimuthal anchoring of ferroelectric liquid crystals by measuring the azimuthal angle of the chevron C2 structure. By varying not only the alignment but also the ferroelectric liquid-crystal layer thickness, we also studied the influence of the ions screening the polarization charge on the chevron layer structure. A simple model describing the free enthalpy of the system was used to calculate the anchoring coefficient from the azimuthal angle of the structure. [ABSTRACT FROM AUTHOR]

The dynamic response of ferroelastic twins to an alternating stress has been studied in situ at high temperature using a stroboscopic x-ray diffractometer and combined dynamical mechanical analyzer (XRD-DMA). The XRD-DMA is designed to allow x-ray rocking curves to be collected while the sample is undergoing simultaneous dynamical mechanical analysis in three-point-bend geometry. The detection of diffracted x-rays is synchronized with the applied load, so that rocking curves corresponding to different parts of the dynamic load cycle can be obtained separately. The technique is applied to single-crystal LaAlO[sub 3], which undergoes a cubic to rhombohedral phase transition at 550 °C, leading to the generation of characteristic “chevron” twins. The rocking-curve topology is calculated as a function of crystal orientation for each chevron type. Systematic changes in the rocking curves during heating and cooling under dynamic load demonstrate a clear preference for chevrons containing {100}[sub pc] walls perpendicular to the sample surface and {110}[sub pc] walls oriented at 45° to the sample surface. These domain walls are oriented favorably with respect to the applied stress (i.e., they separate domains with contrasting components of spontaneous strain parallel to the sample length). Below 200 °C, the superelastic strain is accommodated by rapid advancement/retraction of vertical {100}[sub pc] needle domains, with little effect on the dynamic rocking curves. Above 200 °C, a dynamic shift in peak position between rocking curves measured at the maximum and minimum applied loads is detected. The onset of a dynamic response correlates with the loss of the {100}[sub pc] needle domains and the transformation of the microstructure to 45° {110}[sub pc] walls. Superelastic strain is then accommodated by domain wall displacement/rotation, causing the wall to sweep back and forth across the x-ray beam and diffraction to occur from alternate domains at the maximum and minimum points of the stress cycle. A second sample, oriented so that domain walls in all possible chevrons are unfavorably oriented with respect to the applied stress, shows very different behavior. The rocking curves consist of several well-separated peaks at the minimum load and a single broad diffraction signal at the maximum load. This is caused by the creation of a very high density of twin walls across the sample above a critical applied stress, leading to corrugation of the sample surface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper presents design and analysis of microelectromechanical system (MEMS) based displacement amplification mechanism actuated using thermal actuators with enhanced performance. The proposed model consists of chevron shaped thermal actuators, an amplification mechanism capable of amplifying displacement 20 times and an electrostatic comb drives for sensing displacements. When voltage is applied to thermal chevrons, displacement is produced which is then amplified 20 times. Steady state static thermal electrical analysis is performed under variable resistivity and voltage bias of 2 V. In-plane reaction forces of magnitude 194.2 and 150.91 µN along X and Y-axis, respectively, thus producing displacement of 0.11 and 2.22 µm along X and Y-axis, respectively. Time domain simulations of device are carried with constant electrical resistivity, variable voltage and convective boundary conditions. Modal analysis of the mechanism is carried out to predict the natural frequencies and associated mode shapes of mechanism during free vibrations. The desired mode is at frequency of 286.160 kHz. Dynamic simulations including direct integration-transient, transient modal and steady state modal analysis are performed on the device for time span of 0.0006 s, under application of 25 g and frequency range of 200-300 kHz. Simulation results prove the viability of the mechanism as an amplification device with enhanced voltage-stroke ratio. [ABSTRACT FROM AUTHOR]

The International Society for Rock Mechanics has suggested three chevron notched specimens (CB, SR and CCNBD) to measure mode I fracture toughness of rocks; however, the measured results are not comparable. In this study, the dimensionless stress intensity factors for the three ISRM-suggested specimens are calibrated and demonstrated to be either overestimated, reliable or underestimated. For the first time, the lengths of fracture process zones (FPZs) in these specimens are estimated and revealed to be partly responsible for the measuring discrepancy among these methods. Some controversies about the fracture toughness measurement using the CCNBD specimen are clarified. [ABSTRACT FROM AUTHOR]

An experimental study of the airframe noise for small-scale wing models with high-lift devices (slat and flap) is performed. It is shown that installation of chevrons on the lower edge of a slat leads to noise reduction on both straight and swept wings. Simultaneous acoustic and aerodynamic measurements show that chevrons lead to suppression of the slat tonal noise components without significantly affecting the wing aerodynamics. [ABSTRACT FROM AUTHOR]

Results are presented for experiments investigating the impact of chevrons on overexpanded and subsonic jet plumes and associated acoustic radiation. Faceted, bi-conic convergent-divergent nozzles with design Mach numbers equal to 1.51 and 1.65 are used in the experiments. A design space of nine chevrons with a range of penetrations, lengths and widths are investigated. Low-penetration chevrons are shown to have limited impact on broadband and shock-associated noise for all jet Mach numbers investigated. High-penetration chevrons produce significant peak-noise reduction (relative to the baseline nozzle) in the peak-jet-noise direction with greater noise reduction for subsonic than for supersonic exhausts. High-penetration chevrons are found to increase broadband-shock-associated noise for the highest Mach number jet investigated. While particle image velocimetry results indicate chevrons introduce axial vorticity at all jet conditions, the associated mixing is limited for supersonic exhausts relative to that for subsonic exhausts due to the strong and periodic radial velocity components associated with the jet-shock-cell structure. The introduction of chevrons modifies the near-nozzle shock-cell structure and the impact of internally (within the nozzle) generated shocks on the shock-cell structure generated in the jet plume. The modifications in the near-nozzle shock-cell structure can lead to increased broadband-shock-associated-noise levels for some operating conditions. [ABSTRACT FROM AUTHOR]

The titanosaur sauropodBonatitan reigiis redescribed. The material collected, originally interpreted as pertaining to two different individuals, is reorganised in five individuals, and the original type specimen is separated into three different individuals. One of the braincases is designated as a new type specimen. Some materials are described by the first time (sacral ribs, distal caudal, chevrons, metacarpals, astragalus and metatarsals), others reinterpreted as different bones (‘ulna’ and ‘radius’). The diagnosis ofB. reigiis emended, removing some of the original characters (longitudinal groove located on the suture between the parietals that continues posteriorly over the supraoccipital to the foramen magnum) and adding some new (small paired pits on the frontals and posterior ridge of the metacarpal IV). The phylogenetic analysis does not supportB. reigias a member of the Saltasaurinae, but rather as a basal member of a broad clade of sauropods that in turn is recovered as the sister group of the Saltasauridae. [ABSTRACT FROM PUBLISHER]

A polynomial preserving recovery technique is applied to an overpenalized symmetric interior penalty method. The discontinuous Galerkin solution values are used to recover the gradient and to further construct an a posteriori error estimator in the energy norm. In addition, for uniform triangular meshes and mildly structured meshes satisfying the ε-σ condition, the method for the linear element is superconvergent under the regular pattern and under the chevron pattern, while it is superconvergent for the quadratic element under the regular pattern. [ABSTRACT FROM AUTHOR]

This article questions the application of Chevron deference in federal court habeas review of statutory immigration detention challenges. Since the enactment of a mandatory detention statute for immigrants facing deportation, the Board of Immigration Appeals--an administrative body within the U.S. Department of Justice--has played an increasingly important role in interpreting the scope of detention for thousands of immigrants each year. Federal courts have long served as an important check against executive detention through habeas review and have declined to accommodate other deference norms in the immigration detention context. Federal courts have nonetheless applied Chevron to immigration detention cases without questioning whether such deference to the agency is appropriate. This article explains why federal courts should reject the application of Chevron when exercising habeas review of statutory immigration detention challenges. This article further explains that federal courts, whether or not fettered by Chevron, should apply interpretive norms that properly account for the important physical liberty interest at stake. [ABSTRACT FROM AUTHOR]

The Riemann problem for the shallow water model on a rotating attracting spherical zone numerically is solved. A shock-capturing difference scheme is constructed that approximates the system of conservation laws describing discontinuous solutions of the given model. The Riemann problem is formulated as one of developing a wave process from initial data representing a spherical zone covered by various equilibria and zonal flows. Two Riemann problems are numerically simulated: the breakdown of water 'ridges' of various shapes at equilibrium and propagation of contact discontinuity perturbations between an equilibrium and a zonal flow. The general properties of such solutions independent of the geometric configuration of the domains occupied by elementary solutions in the initial data are demonstrated. [ABSTRACT FROM AUTHOR]

In this study, the theoretical results of energy and exergy analyses of the chevron type heat exchanger are compared with experimental ones. A test ring is set up and water is used as working fluid. While mass flow rate of hot water was kept constant as 0.083 kg s −1 , the mass flow rate of cold water varies from 0.027 kg s −1 to 0.083 kg s −1 , the hot water temperature from 35 to 60 °C, cold water temperature from 21 to 25.35 °C in the experiments. The energy efficiency increases linearly with respect to hot water inlet temperature at the cold water mass flow rate values, however, in exergy efficiency, the optimum conditions comes out. Energy efficiency of the chevron type heat exchanger has the theoretical and experimental values ranging from 45% to 78%. When it comes to the exergy efficiency of the chevron type, the heat exchanger has the theoretical values ranging from 16% to 39.5% and experimental values from 13% to 47.8%. It is found that the theoretical results have a good agreement with the experimental ones. [ABSTRACT FROM AUTHOR]

The three methods of determining the quasi-static Mode I fracture toughness ( KIc) (surface crack in flexure-SC, single-edge precracked beam-PB, and chevron-notched beam-VB) found in ASTM C1421 were applied to a variety of advanced ceramic materials. All three methods produced valid and comparable KIc values for the Al2O3, SiC, Si3N4, and SiAlON ceramics examined. However, not all methods could successfully be applied to B4C, ZrO2, and WC ceramics due to a variety of material factors. The coarse-grained microstructure of one B4C hindered the ability to observe and measure the precracks generated in the SC and PB methods while the transformation toughening in the ZrO2 prevented the formation of the SC and PB precracks and thus made it impossible to use either method on this ceramic. The high strength and elastic modulus of the WC made it impossible to achieve stable crack growth using the VB method because the specimen stored a tremendous amount of energy prior to fracture. Even though these methods have passed the rigors of the standardization process there are still some issues to be resolved when the methods are applied to certain classes of ceramics. It is recommended that, when appropriate, at least two of these methods be employed to determine the KIc, especially when a new or unfamiliar ceramic is being evaluated. [ABSTRACT FROM AUTHOR]

An energy-based model is developed to describe the periodic formation of voids/saddle reefs in hinge zones of chevron folds. Such patterns have been observed in a series of experiments on layers of paper, as well as in the field. A simplified hinge region in a stack of elastic layers, with straight limbs connected by convex segments, is constructed so that a void forms every $$m$$ layers and repeats periodically. Energy contributions include strain energy of bending and work done both against a confining overburden pressure and an axial compressive load. The resulting total potential energy functional for the system is minimised subject to the constraint of non-interpenetration of layers, leading to representation as a nonlinear second-order free boundary problem. Numerical solutions demonstrate that there can exist a minimum-energy $$m$$ -periodic solution with $$m \ne 1$$ . The model shows good agreement when compared with experiments on layers of paper. [ABSTRACT FROM AUTHOR]

Conchological Variability of Anadara inaequivalvis (Bivalvia, Arcidae) in the Black-Azov Sea Basin. Anistratenko, V. V., Anistratenko, O. Yu., Khaliman, I. A. - An alien species in the Black Sea and the Sea of Azov - Anadara inaequivalvis (Bruguiere, 1789) - was recently discovered to have a wide range of shell variability. From the investigated samples (over 900 valves) six basic types of the shell commissural opening were defined; they are not, however, discrete conditions. Th e presence of intermediate variants reveals a gradual (continuous) character of the shell variability and indicates that all the samples investigated belong to the same species. Th e variation of some other Anadara characteristics is also discussed, including: quantity and ornamentation of the ribs on the surface of the valves, quantity of chevrons on the ligament area, shape of the hinge plate and quantity of hinge teeth. A comparison of conchological characteristics of Anadara from the Black-Azov Sea Basin with A. inaequivalvis from southeast India shows that ranges and patterns of shell variability of Azov-Black Sea Anadara correspond to variability of A. inaequivalvis from this species type locality - Coromandel Coast of India. [ABSTRACT FROM AUTHOR]

Background Supracondylar intercondylar fractures of the humerus have been treated surgically by various methods using standard approaches. But none of the authors have reported fixation of these fractures with a Y plate. In this study we report the functional outcomeof a series of patients with supracondylar-intercondylar fractures treated by Y plate fixation, using a standard approach. Materials & Methods 18 adult patients with supracondylar-intercondylar fractures of humerus admitted in our institution between August 2009 and November 2010 were treated with open reduction and internal fixation with Y plate. These plates were ideally designed for the fixation of calcaneal fractures. A standard posterior approach with Chevron osteotomy was used for a better visualisation of the articular fragments. Patients with medical contraindications for surgery, those with paralytic disease of the injured elbow, pre-existing disease or deformity of the elbow, vascular injury at elbow and those with pathological fractures were excluded from the study. Clinical assessment include pain, range of movements, stability of elbow and activities of daily living. The Mayo Elbow Performance Score (MEPS) was used as criteria to evaluate the functional outcome. Statistical analysis was performed with the help of the biostatistical department in our institution. Results Out of 18 cases, nine cases (50%) were type C2 according to the classification by Mullers et al, 5 were type C3 (27.7%) and 4 (22.2%) were C1 type. Three open fractures were encountered of which two were type C2 and one was type C3. The mean age of the patient was 40.83 (23-68 years). The average duration of follow up was 28.8 months (range 24-36 months). The mean period for solid radiological fracture union was 16 weeks. The Mayo Elbow Performance Score was used to evaluate the functional result in C1, C2 and C3 fractures and was found to be 90, 87 and 76 respectively. Conclusion Supracondylar-intercondylar fractures of humerus in adults, treated by the method of Y plate fixation is a good and easy method of fixation with a good functional outcome. [ABSTRACT FROM AUTHOR]

This work focuses on the noise reduction capabilities of chevrons, fluidic injection, and a combination of both. The control mechanisms were experimentally investigated for over, under, and ideally expanded operating conditions. Acoustic far-field data was collected to quantify noise reductions and changes to the flow field through use of theoretical relations. Results show appreciable noise reduction by both fluidic injection and chevrons. Optimal performance of the two technologies occured at opposite ends of the operation envelope, with the chevrons performing better in the underexpanded regime and the fluidics in the overexpanded regime. The combination of the two technologies was also shown to achieve substantial noise reduction, but direct additive benefits were not always gained. This result is still important as it shows fluidic injection can be employed on complex geometry nozzles, such as that on the F-35, and still achieve noise reduction. [ABSTRACT FROM AUTHOR]

The article focuses on the role of legitimacy in expertise of Chevron doctrine. It discusses various aspects related to the Chevron doctrine, application in public administration and administrative procedures. It further explains the role of the doctrines in expertise aspects of judgment, understanding and evaluating the judgment and its applications on various other judgments.

The article focuses on various aspects of Chevron deference doctrine. It discusses various cases and aspects defining their boundaries around the applicability of the doctrine and also discusses the two step method employed for eliminating the confusion related to these doctrines. Various topics discussed include statutory constructions, deference and amendments made.

Objective: To assess interfacial fracture toughness of different adhesive approaches and compare to a standard micro-tensile bond-strength (μTBS) test. Methods: Chevron-notched beam fracture toughness (CNB) was measured following a modified ISO 24370 standard. Composite bars with dimensions of 3.0×4.0×25mm were prepared, with the adhesive–dentin interface in the middle. At the adhesive–dentin interface, a chevron notch was prepared using a 0.15mm thin diamond blade mounted in a water-cooled diamond saw. Each specimen was loaded until failure in a 4-point bend test setup and the fracture toughness was calculated according to the ISO specifications. Similarly, adhesive–dentin micro-specimens (1.0×1.0×8–10mm) were stressed in tensile until failure to determine the μTBS. Results: A positive correlation (r 2 =0.64) was observed between CNB and μTBS, which however was only nearly statistically significant, mainly due to the dissimilar outcome of Scotchbond Universal (3M ESPE). While few μTBS specimens failed at the adhesive–dentin interface, almost all CNB specimens failed interfacially at the notch tip. Weibull moduli for interfacial fracture toughness were much higher than for μTBS (3.8–11.5 versus 2.7–4.8, respectively), especially relevant with regard to early failures. Significance: Although the ranking of the adhesives on their bonding effectiveness tested using CNB and μTBS corresponded well, the outcome of CNB appeared more reliable and less variable. Fracture toughness measurement is however more laborious and requires specific equipment. The μTBS nevertheless appeared to remain a valid method to assess bonding effectiveness in a versatile way. [ABSTRACT FROM AUTHOR]

Abstract: Three engineering treatments were implemented in a driving simulator study to assess the effect of road-based measures on alleviating the symptoms of fatigue. Using results from previous research on the effect of circadian rhythms on fatigue-related crashes, two groups of male drivers were recruited for this study: young shift workers under the age of 35, who attended immediately after their night shift, and older drivers over the age of 45, who completed the study during the ‘post lunch dip’ period, after consuming lunch. Eye tracking (PERCLOS) and lateral driver performance measures were used to assess whether baseline measures of fatigue changed after drivers experienced each of the three treatments, which included variable message signs, chevrons and rumble strips. Results showed a marked difference in these measures between drivers’ baseline (not fatigued) and experimental (fatigued) visits. There were also some reductions in lateral deviation and eye closure (as measured by PERCLOS) when the treatments were encountered, but no marked difference between the three treatments. These results suggest that in addition to driver- and vehicle-based methods currently employed to mitigate the effects of fatigue, the inclusion of such engineering measures may help alleviate fatigue-related impairments in driving, particularly if such treatments are implemented during long stretches of straight monotonous roads which are known to be associated with fatigue-related crashes. However, positive effects of the treatments were short lived, prompting the need for further investigations on their optimal frequency of presentation and combination to achieve maximum impact from these low-cost, road-based treatments. [Copyright &y& Elsevier]

A general method for facilitating the interpretation of computer simulations of protein folding with minimally frustrated energy landscapes is detailed and applied to a designed ankyrin repeat protein (4ANK). In the method, groups of residues are assigned to foldons and these foldons are used to map the conformational space of the protein onto a set of discrete macrobasins. The free energies of the individual macrobasins are then calculated, informing practical kinetic analysis. Two simple assumptions about the universality of the rate for downhill transitions between macrobasins and the natural local connectivity between macrobasins lead to a scheme for predicting overall folding and unfolding rates, generating chevron plots under varying thermodynamic conditions, and inferring dominant kinetic folding pathways. To illustrate the approach, free energies of macrobasins were calculated from biased simulations of a non-additive structure-based model using two structurally motivated foldon definitions at the full and half ankyrin repeat resolutions. The calculated chevrons have features consistent with those measured in stopped flow chemical denaturation experiments. The dominant inferred folding pathway has an "inside-out", nucleation-propagation like character. [ABSTRACT FROM AUTHOR]

In the tails of dromaeosaurid dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally. The fully articulated and three-dimensionally preserved caudal series of some dromaeosaurid specimens show that individually these caudal rods were flexible, not rigid as previously thought. However, examination of the arrangement of the caudal rods in cross-section indicates that the combined effect of multiple caudal rods did provide substantial rigidity in the dorsoventral, but not in the lateral, plane. The results of digital muscle reconstructions confirm that dromaeosaurids and rhamphorhynchids also shared greatly reduced caudofemoral muscles in the anterior tail region. The striking similarities between the tails of dromaeosaurids and rhamphorhynchids suggest that both evolved under similar behavioral and biomechanical pressures. Combined with recent discoveries of primitive deinonychosaurs that phylogenetically bracket the evolution of dromaeosaurid caudal rods between two arboreal gliding/flying forms, these results are evidence that the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle. [ABSTRACT FROM AUTHOR]

This paper describes a joint experimental and computational study of the Mow field and acoustics of conical Convergent--divergent nozzles such as those found on high-performance military aircraft. The influence of chevrons on a nozzle with an area ratio corresponding to a design Mach number of 1.5 (design pressure ratio of 3.67) is examined. The nozzle is tested at its design condition, at overexpanded conditions with pressure ratios of 2.5, 3.0, and 3.5 and at underexpanded conditions with pressure ratios of 4.0, 4.5, and 5.0. Each case is compared to a baseline nozzle at the same condition without chevrons. Shadowgraph images show that chevrons reduce the shock cell spacing. Near-field acoustic measurements show that sources of broadband shock-associated noise move downstream when chevrons are applied. Near-field acoustics also reveal that, for supersonic jets, chevrons produce significant noise near the nozzle exit across the whole range of frequencies. Far-field acoustic measurements show that the application of chevrons reduces screech, broadband shock-associated noise, and mixing noise, except for frequencies above the broadband shock-associated noise peak for overexpanded and perfectly expanded conditions. [ABSTRACT FROM AUTHOR]

This paper compares the design and performance of kink actuators, a modified version of the bent-beam thermal actuator, to the standard chevron-shaped designs. A variety of kink and chevron actuator designs were fabricated from polysilicon. While the actuators were electrically probed, these designs were tested using a probe station connected to a National Instruments (NI) controller that uses LabVIEW to extract the displacement results via image processing. The displacement results were then used to validate the thermal-electric-structural simulations produced by COMSOL. These results, in turn, were used to extract the stiffness for both actuator types. The data extracted show that chevron actuators can have larger stiffness values with increasing offsets, but at the cost of lower amplification factors. In contrast, kink actuators showed a constant stiffness value equivalent to the chevron actuator with the highest amplification factor. The kink actuator also had larger amplification factors than chevrons at all designs tested. Therefore, kink actuators are capable of longer throws at lower power levels than the standard chevron designs. [ABSTRACT FROM AUTHOR]

A new concept of reducing the noise of a slat by applying a chevron form to the bottom edge is experimentally verified. The results of parametric studies are presented, which have been carried out on a small-scale model of a part of the wing (a scale of 1: 18) with deflected high-lift devices (the slat and the flap) in the landing configuration. As a result of acoustic measurements, a decrease (up to 4.5 dB) in narrowband noise for some chevron geometries is observed in comparison to a usual slat. The value of the decrease is a complex function of frequency, the wing and slat geometry, and the flow characteristics. [ABSTRACT FROM AUTHOR]

Sauropod haemal arches are caudal bony structures that have been traditionally incorporated into two different types observed in different anatomical views: Y-shaped (anterior view) and forked (lateral view). This research proposes a classification combining information observed in anterior and lateral views. Four types of ‘Y-shaped’ and six types of ‘V-shaped’ chevrons were recognised. Complete chevron series in some eusauropods allows the comparison of topological equivalent structures along the tail and also among taxa. A basal titanosaur from Argentina exhibits mid-caudal chevron morphology in which more than one cranial and caudal process is present, arising from the distal blades as well as from the proximal rami, a condition not seen before in a sauropod dinosaur. The morphological variability seen in sauropod chevrons along the tail is in close relationship with the development and distribution of muscle. caudofemoralis longus, as seen in extant crocodiles and as previously proposed for non-avian theropods and for caudal centra and transverse processes of sauropod dinosaurs. Two new characters related to middle chevrons are proposed here, in which the transitional morphology is described. [ABSTRACT FROM AUTHOR]

We present a continuous space model for travel in a unit-load warehouse that allows cross-aisles and picking aisles to take on any angle. The model produces optimal designs for one, two, and three-cross-aisle warehouses, which are called chevron, leaf, and butterfly designs. We then use a more accurate discrete model to show which designs are best for a wide range of warehouse sizes. We show that the chevron design, which is new to theory and to practice, is the best design for many industrial applications. [ABSTRACT FROM PUBLISHER]

Abstract: Condensation pressure drop of carbon dioxide in brazed plate heat exchangers was investigated, and is presented in this paper. Carbon dioxide is known as an environmental friendly refrigerant with an Ozone Depletion Potential (ODP) equal to zero and Global Warming Potential (GWP) equal to unity, and has favorable thermodynamic and transport properties though it requires higher operating pressures (∼15–30bar). Brazed-type plate heat exchangers that can withstand high pressure are a good choice for such applications. This paper presents the procedure, data collection, and results for three brazed plate heat exchangers with different inner geometries. The test exchangers showed good performance at high system pressures with reasonable pressure drops (less than 8%). The collected experimental data that covered real world operating conditions are valuable for the design of cascade condensers with carbon dioxide as the low-side refrigerant. [Copyright &y& Elsevier]

Advances in block copolymer directed assembly have highlighted the potential of block copolymer lithography to define patterned templates for magnetic recording bit patterned media (BPM). The naturally periodic features found in block copolymer films display superior size uniformity at ultrahigh densities, making them ideal lithographic masks to define the highly periodic data bits in the data sector of hard disk drives. In addition to the data bits, BPM architecture requires additional features to encode servo information. Because of the nature of the information stored in servo sectors, the geometry and shape of servo features differ from those in the data sectors, potentially compromising their compatibility with the features that can be naturally formed by block copolymers. The authors investigated the compatibility of a block copolymer directed assembly with the formation of complex chevron structures for sector header servo patterns within the framework of a BPM design that uses rectangular bits as the storage units. In order to ensure proper registration between the data tracks and the chevron patterns, the authors propose a design that employs lamellae-forming block copolymers assembled on chemical patterns with density multiplication into sets of lines that define both the data tracks and the servo features simultaneously. Due to the high free energy penalty associated with bending the lamellar domains, the block copolymer formed defective structures at the apex of the chevrons, as well as in the junction areas between chevrons and periodic horizontal lines. Adding stripes to the design of the chemical patterns near these complex areas prevented defects from propagating into the periodic line areas. In addition, the predictable defective structure offered flexibility for subsequent signal processing such as track identification and head position correction. [ABSTRACT FROM AUTHOR]

'Chevrons', a sawtooth pattern on the trailing edge of exhaust nozzles, are being implemented on modern jet engines. The technology reduces jet noise for 'separate-flow' nozzles used on newer jet aircraft engines. The purpose of this paper is to describe the development of this technology, starting with studies of 'tabs' in the 1980's and 1990's. The tabs, essentially chevrons with more aggressive penetration, were studied in those early years with a focus on mixing enhancement in jets. Observations from experimentalists in connection with mixing enhancement and plume signature reduction suggested that there might also be a noise benefit. In the mid-nineties, these devices, with mild penetration to minimize thrust loss, were first seriously explored for aircraft engine noise reduction purposes. Prompted by a strong need for jet noise reduction, the study became a joint NASA/industry effort that ultimately matured the chevron technology to production by mid-2000's. The process is an example of how fundamental studies over decades eventually migrate to application but often take a concerted effort. [ABSTRACT FROM AUTHOR]

We report results from the simulation of a moderate Reynolds number cold jet flow exhausting from a chevron nozzle with six symmetric chevrons that have an approximately 18-degree penetration angle. The flow inside the nozzle geometry and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large eddy simulation code with overset grid capability. The simulation is performed on 400 million grid points using 2048 processor cores in parallel. The main emphasis of the simulation is to compute the jet flow in maximum detail possible and accurately capture the physical processes that lead to noise generation. It is especially critical to capture the enhanced shear layer mixing due to chevrons that takes place within the first few diameters downstream of the nozzle exit. Our calculations resolve the jet flow field at an unprecedented level of detail. Despite some issues such as an order of magnitude lower simulation Reynolds number (relative to experimental value) and unknown turbulence intensity levels within the experimental nozzle, it is shown that both the near-field jet turbulence and far-field noise predictions are in good agreement with the experimental measurements. Because of the enormous number of grid points required to resolve the near-nozzle region, the computational domain size is constrained to ten nozzle exit diameters downstream of nozzle exit by the limited computational resources. As a result, not all of the low frequency generating noise sources are resolved in the calculation, resulting in some errors in the low frequency range of the predicted noise spectrum. Nevertheless, it is shown that the high frequency noise generation in the near-nozzle region is predicted quite well. [ABSTRACT FROM AUTHOR]

Localized arc filament plasma actuators (LAFPAs) have been used to control the flow and farfield acoustics of high Reynolds number, high-speed unheated jets at the Gas Dynamics and Turbulence Laboratory. The jet facility consists of an axisymmetric jet of exit diameter 2.54 cm with different nozzle blocks and variable jet temperature in an anechoic chamber. The focus of this paper is on the effect of control on far-field noise in a high subsonic (Mj = 0.9) jet over a wide range of temperatures. A total of sixteen combinations of forcing azimuthal modes (m = 0, 1, 3, and ±4) and temperature ratios (To/Ta = 1.0, 1.5, 2.0, and 2.5) at a wide range of forcing frequencies were utilized to explore LAFPAs' effect on far-field noise. LAFPAs show significant noise reduction around the peak frequency in shallow angles and a small increase in higher frequencies. The level of reduction is lower and the level of increase is higher towards the sideline. Consistent with previous works, the results show that forcing with higher azimuthal modes produces greater noise reduction. LAFPAs produce large amplitude narrowband tones in this small jet that are believed to be less significant in larger jets. The impact of these forcing tones is isolated and discussed. Across the range of temperatures explored, the effectiveness of LAFPAs improves as temperature increases. Possible reasons for the increase in effectiveness are discussed. [ABSTRACT FROM AUTHOR]

Tests were conducted to determine the effect of chevrons on the sound radiated from the exhaust of a Mach 1.19 core flow with simulated flight effects. Flight effects were studied by using a secondary coaxial flow varied from static to Mach 0.50. Shadowgraphy, static pressure, and turbulence measurements were used to complement near-field pressure and far-field acoustic measurements. The presence of a secondary flow causes the shock-cell length to slightly lengthen and the shock cells to persist farther downstream; this was true for both the baseline and chevron nozzles. Compared with the baseline nozzle, the shadowgraphy and near-field static pressure showed that the chevrons reduced the shock-cell spacing with minimal effect on the shock-cell strength. Higher turbulence levels near the nozzle exit and comparable shock-cell strength led to higher shock-associated noise for the chevron configuration compared with the baseline. The decrease in shock-cell length caused the peak amplitude of the shock-associated noise to shift to higher frequencies. At the same time, the chevrons significantly reduced any screech tones that were initially present for the baseline case. Finally, it was shown that the chevrons reduced turbulence levels near the end of the potential core, which resulted in a reduction of the low-frequency mixing noise that dominates the aft angles. [ABSTRACT FROM AUTHOR]

The article discusses Canadian reactions towards the British War Office's use of overseas service chevrons to honor the foreign military service of the British Empire's expeditionary forces during World War I. While initially disliked, the author explains that Canadian veterans came to embrace the chevrons as markers of their military careers. The author explains the symbolic importance of military badges, medals, and insignia, and specifically details how the overseas service chevrons affected the identity of Canadian soldiers and Canadian national identity generally.

Propagation of solitary waves activated in thin ferroelectric liquid crystal cells under external, sinusoidally alternating electric fields is investigated using the electro-optic technique. It is shown that solitons give contributions only to the loss component of the response spectrum, within rather narrow ranges of frequencies and in sufficiently strong fields. The limit frequency, at which the amplitude of the velocity of the solitary waves is greatest, is found to be related to material constants of liquid crystals. Measuring this threshold frequency provides the capability to determine the elastic constant of surface stabilized liquid crystalline materials in the bookshelf or chevron layer geometries. [ABSTRACT FROM AUTHOR]

Abstract: The experimental investigation of carbon dioxide condensation in brazed plate heat exchangers is the main objective of this study. The current level of concern for the environment is at an all time high, therefore, it is important to look into methods and resources that lead to a cleaner and healthier future for the planet. This study details one such effort to reach this goal, focusing on condensation of carbon dioxide as a natural refrigerant in refrigeration systems. Three brazed plate heat exchangers with different geometry, each consisting of three channels, are tested. This paper focuses on the two-phase analysis, where carbon dioxide was the working fluid, flowing through the middle channel, and dynalene brine, the cooling fluid, flowed through the side channels of each geometry. Condensation of carbon dioxide occurred at saturation temperatures ranging from −17.8°C to −34.4°C and heat fluxes spanning 2.5–15.7kW/m2. An in-depth dimensional analysis was completed on the two-phase data yielding heat transfer correlations. Relationships of the two-phase heat transfer characteristics are presented, the data are compared with related studies, and conclusions are made from the two-phase data. [Copyright &y& Elsevier]

The spatial structure of the flow in a supersonic underexpanded jet exhausting from a convergent nozzle with vortex generators (chevrons) at the exit is experimentally studied. Disturbances of two types are observed during interaction of a single chevron and the main jet. The stronger disturbance is caused by the presence of the wake component and by generation of two streamwise vortices. The weaker disturbance is manifested in the form of perturbations of the Mach wave type propagating in the supersonic part of the shear layer of the main jet. Interaction of the set of chevrons with the jet flow leads to transformation of the stationary jet structure and to formation of mushroom-shaped large-scale vortex structures. The experimental and numerical data are demonstrated to be in reasonable agreement. [ABSTRACT FROM AUTHOR]

The spatial structure of the flow in a supersonic underexpanded jet exhausting from a convergent nozzle with vortex generators (chevrons) at the exit is experimentally studied. Exhaustion of a supersonic underexpanded jet from a nozzle with chevrons at the nozzle exit is numerically simulated with the use of the Fluent commercial software package. The experimental and numerical data are demonstrated to be in reasonable agreement. The influence of chevrons on the process of gas mixing is estimated. [ABSTRACT FROM AUTHOR]

The first Diplothrix (Muridae, Rodentia) fossils of the early Early Pleistocene are described as D. yangziensis sp. nov., which were collected from the Renzidong Cave deposits in Anhui Province, Eastern China. Diplothrix was previously represented by a single species, D. legata, whose geographical distribution during the Late Pleistocene is restricted to the Ryukyu Islands, Japan. With straight chevrons on M1, distinct t3 and t9 on upper molars, primitive M3, mlc on m1, and developed a-lab on m2 and m3, the new species is morphologically distinct from other large murids in East Asia, and should belong to the genus Diplothrix. There are also differences in molar morphology between the new species and D. legata, the type species of Diplothrix, as well as other known fossils. For example, D. yangziensis sp. nov. has a smaller size, a more elongated crown, developed precingulum and pc on M1, more primitive M3, weaker mlc and more primitive pc on m1, and stronger plc and pc on m3. In short, Diplothrix yangziensis sp. nov. is evidently more primitive than D. legata, suggesting that the former is likely the ancestor of the latter. Diplothrix yangziensis sp. nov. is the first discovery of the genus outside the Ryukyu Islands, Japan and is also the earliest and most primitive species of the genus in Eurasia. Its discovery has significant implications for reconstructing the evolution and dispersal pattern of Diplothrix, as well as for discussing its palaeoecological variation. [ABSTRACT FROM AUTHOR]

Fabrication of operable surface-stabilized ferroelectric liquid crystals (SSFLCs) is often hampered by the occurrence of zigzag defects. This defect formation can, to some extent, be controlled or eliminated in SSFLCs in which the rubbing directions are set parallel, because two chevrons have different molecular alignment structures and different energies. In this study, we try to fabricate a defect-free SSFLC with anti-parallel rubbed films which possess different surface anchoring and/or pretilt angle between two cell substrates in order for the energy condition in two types of chevron to be different. In the case using a combination of the same alignment film material, it was confirmed that in all alignment film materials used in this research, the occurrence of zigzag defects can be reduced as the difference of rubbing strengths increases between two alignment films. It is found that the appearance of zigzag defects can be more strongly suppressed as the difference of pretilt angles increases between two alignment films, and then in the case of the large difference, zigzag defect-free SSFLCs can be obtained. Furthermore, it is found that the effect of the pretilt on the suppression of zigzag defect is much stronger than that of the anchoring strength. [ABSTRACT FROM AUTHOR]

In this research, a seismic retrofitting method for chevron-braced frames (CBFs) is proposed. The key idea here is to prevent the buckling of the chevron braces via a conventional construction technique that involves a hysteretic energy-dissipating element installed between the braces and the connected beam. The energy-dissipating element is designed to yield prior to buckling of the braces, thereby preventing the lateral stiffness and strength degradation of the CBF caused by buckling, while effectively dissipating the earthquake input energy. Nonlinear static pushover, time history and damage analyses of the CBF and retrofitted CBF (RCBF) are conducted to assess the performance of the RCBF compared with that of the CBF. The results of the analyses reveal that the proposed retrofitting method can efficiently alleviate the detrimental effects of earthquakes on the CBF. The RCBF has a more stable lateral force–deformation behavior with enhanced energy dissipation capability than the CBF. For small-to-moderate intensity ground motions, the maximum interstory drift of the RCBF is close to that of the CBF. But, for high intensity ground motions, it is considerably smaller than that of the CBF. Compared with the CBF under medium-to-large intensity ground motions, the RCBF experiences significantly less damage due to prevention of buckling of the braces. [ABSTRACT FROM AUTHOR]

Abstract: Numerical simulations of round, compressible, turbulent jets using the Shear Stress Transport (SST k–ω) model have been carried out. The three-dimensional calculations have been done on a tetrahedral mesh with 0.9 million cells. Two jets, one cold and hot, have been simulated. The Mach number for both the cases is 0.75. Overall sound pressure levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams–Hawkings equation. The numerical predictions have been compared with experimental results available in the literature. Axial and radial variation of the mean axial velocity, axial variation of , radial variation of and overall SPL levels are compared. The potential core length is predicted well, but the predicted centerline velocity decay is faster than the measured value. The URANS calculations are not able to predict the absolute values for the overall SPL, but predict the trends reasonably well. The calculations predict the trends and absolute values of the variations of the spectral amplitude well for the aft receivers, but not for the forward receivers. Effect of chevrons on the noise from the jet is also investigated for cold and hot jets. In each case, two chevron taper angles, namely, 0° and 5° are considered. The latter nozzle produces the most significant modification to the baseline spectra and is less effective at high frequencies in abating the noise. The present calculations predict a reduction in the overall SPL for the chevron nozzle with 0° taper angle and a slight increase for chevron nozzle with 5° taper angle, for both cold and hot jets. [Copyright &y& Elsevier]

The study of fluid inclusions in Lower Triassic Röt halite from the Rockensussra 2/83 borehole in northern Germany showed the presence of primary and secondary gas-liquid inclusions. The gas phase in inclusions indicates their stretching due to salt overheating at some postsedimentary stage. The homogenization temperature of inclusions indicates the overheating temperature of about 60-70°C. The overheating is additionally indicated by trails of migration of large secondary inclusions occurring inside chevrons. The major-ion (K, Mg and SO) composition of inclusion brines was established with the use of ultramicrochemical analysis (UMCA). The results of chemical analyses of brines of primary inclusions in halite from the Rockensussra 2/83 borehole confirm the earlier results for the Röt halite from the Netherlands and Poland. The bromine content in halite is 78-107 ppm, supporting thus marine origin of halite. Brines of primary gas-liquid inclusions are thus representative samples of trapped evaporite water and they may be used for the reconstruction of the composition of Early Triassic seawater. The comparison of our analytical data with the earlier published data and models of chemical composition of seawater during the Phanerozoic which were constructed with the use of the HMW computer program makes it possible to conclude that the Early Triassic seawater was of the SO-rich type and considering the ratios of major ions it fully corresponded to the Early Permian (Asselian-Sakmarian) seawater. It differed from the present seawater by a slight decrease of Na and Mg ions, a considerable decrease of SO ion (by 31%) and an increase of Ca ion (by 36%). [ABSTRACT FROM AUTHOR]

Abstract: Chevron patterns and defect lattices are unique patterns found in the electrohydrodynamic convection of nematic liquid crystals. We study numerically the stability and bifurcations of the chevron patterns and the limit-cycle oscillation of defect lattices using a two-dimensional anisotropic model equation. Simplified one dimensional models are derived by truncating Fourier modes from the two-dimensional model to qualitatively understand the chevron patterns and the defect lattices. The pattern formation and the dynamical behaviors in the one-dimensional models are compared with the numerical simulations of the two-dimensional model. [Copyright &y& Elsevier]