A very efficient RCS data compression and reconstruction technique, volume 4

A very efficient compression and reconstruction scheme for RCS measurement data was developed. The compression is done by isolating the scattering mechanisms on the target and recording their individual responses in the frequency and azimuth scans, respectively. The reconstruction, which is an inverse process of the compression, is granted by the sampling theorem. Two sets of data, the corner reflectors and the F-117 fighter model, were processed and the results were shown to be convincing. The compression ratio can be as large as several hundred, depending on the target's geometry and scattering characteristics

High Input Impedance Voltage-Mode Universal Biquadratic Filters With Three Inputs Using Three CCs and Grounding Capacitors

Two current conveyors (CCs) based high input impedance voltage-mode universal biquadratic filters each with three input terminals and one output terminal are presented. The first circuit is composed of three differential voltage current conveyors (DVCCs), two grounded capacitors and four resistors. The second circuit is composed of two DVCCs, one differential difference current conveyor (DDCC), two grounded capacitors and four grounded resistors. The proposed circuits can realize all the standard filter functions, namely, lowpass, bandpass, highpass, notch and allpass filters by the selections of different input voltage terminals. The proposed circuits offer the features of high input impedance, using only grounded capacitors and low active and passive sensitivities. Moreover, the x ports of the DVCCs (or DDCC) in the proposed circuits are connected directly to resistors. This design offers the feature of a direct incorporation of the parasitic resistance at the x terminal of the DVCC (DDCC), Rx, as a part of the main resistance

Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated

Separation of turbulent, incompressible flow from a curved, backward-facing step

October 1966Includes bibliographical referencesAn experimental investigation of turbulent, incompressible flow separation over curved and sharp, backward-facing steps is presented with results for various step heights. Mean velocities in the separating boundary layer as well as the downstream shear layer were recorded. The static pressure in the separated region was determined with a spherical probe. With the curved step, the boundary layer separated at approximately 28 degrees: the reattachment lengths were somewhat less and the base pressures slightly higher than those with the sharp step.Research carried out under Bureau of Ships General Hydromechanics Research Program, administered by the David Taylor Model Basin contract S-R009 01 01 Nonr 1841(91

NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology

We have measured the effect of uniaxial stress on the threshold field ET for the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1 - e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This ecpression remains valid over more than two decades of ET, up to the highest fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity concentraction. The CDW transition temperature Tp decreases linearly with e at a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov de-Haas measurements show that the extremal area of the Fermi surface decreases with increasing strain. The results suggest that there is an intimate relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure

Embedding a one-column ocean model in the Community Atmosphere Model 5.3 to improve Madden–Julian Oscillation simulation in boreal winter

The effect of the air–sea interaction on the Madden–Julian Oscillation (MJO) was investigated using the one-column ocean model Snow–Ice–Thermocline (SIT 1.06) embedded in the Community Atmosphere Model 5.3 (CAM5.3; hereafter CAM5–SIT v1.0). The SIT model with 41 vertical layers was developed to simulate sea surface temperature (SST) and upper-ocean temperature variations with a high vertical resolution that resolves the cool skin and diurnal warm layer and the upper oceanic temperature gradient. A series of 30-year sensitivity experiments were conducted in which various model configurations (e.g., coupled versus uncoupled, vertical resolution and depth of the SIT model, coupling domains, and absence of the diurnal cycle) were considered to evaluate the effect of air–sea coupling on MJO simulation. Most of the CAM5–SIT experiments exhibit higher fidelity than the CAM5-alone experiment in characterizing the basic features of the MJO such as spatiotemporal variability and the eastward propagation in boreal winter. The overall MJO simulation performance of CAM5–SIT benefits from (1) better resolving the fine vertical structure of upper-ocean temperature and therefore the air–sea interaction that results in more realistic intraseasonal variability in both SST and atmospheric circulation and (2) the adequate thickness of a vertically gridded ocean layer. The sensitivity experiments demonstrate the necessity of coupling the tropical eastern Pacific in addition to the tropical Indian Ocean and the tropical western Pacific. Coupling is more essential in the south than north of the Equator in the tropical western Pacific. Enhanced MJO could be obtained without considering the diurnal cycle in coupling.</p

SplitPocket: identification of protein functional surfaces and characterization of their spatial patterns

SplitPocket (http://pocket.uchicago.edu/) is a web server to identify functional surfaces of protein from structure coordinates. Using the Alpha Shape Theory, we previously developed an analytical approach to identify protein functional surfaces by the geometric concept of a split pocket, which is a pocket split by a binding ligand. Our geometric approach extracts site-specific spatial information from coordinates of structures. To reduce the search space, probe radii are designed according to the physicochemical textures of molecules. The method uses the weighted Delaunay triangulation and the discrete flow algorithm to obtain geometric measurements and spatial patterns for each predicted pocket. It can also measure the hydrophobicity on a surface patch. Furthermore, we quantify the evolutionary conservation of surface patches by an index derived from the entropy scores in HSSP (homology-derived secondary structure of proteins). We have used the method to examine ∼1.16 million potential pockets and identified the split pockets in >26 000 structures in the Protein Data Bank. This integrated web server of functional surfaces provides a source of spatial patterns to serve as templates for predicting the functional surfaces of unbound structures involved in binding activities. These spatial patterns should also be useful for protein functional inference, structural evolution and drug design

Peierls barrier characteristic and anomalous strain hardening provoked by dynamic-strain-aging strengthening in a body-centered-cubic high-entropy alloy

The temperature effect on the mechanical behavior of the HfNbTaTiZr high entropy alloy (HEA) was investigated at 77–673 K. The decrease of the yield strength with increasing the temperature was mechanistically analyzed by considering contributions from various strengthening mechanisms. An anomalous dependence of strain hardening on temperature was observed and was justified to be caused by dynamic strain aging (DSA) as an extra strengthening mechanism at elevated temperatures. A model was constructed to split the overall strain hardening into forest hardening and DSA hardening, both of which were theoretically quantified at all temperatures considered. The work quantifies the height of Peierls barriers in the bcc HfNbTaTiZr HEA, and reveals dynamic strain aging as the strengthening mechanism causing the anomalous strain hardening at elevated temperatures