Gallium arsenide (GaAs)-based photoconductive switches for pulsegeneration and sampling applications in the nanosecond regime

The design is described of a set of optoelectronic switches having an interdigitated electrode structure and implemented with high-resistivity GaAs photoconductive substrates. A theoretical analysis is developed for determining the pulsed light ON-state resistance (peak conductance), OFF-state (dark) resistance, and the associated capacitances for the various designed gap geometries. Data are provided on the processing steps used in successfully fabricating a working set of switches based on the theoretical design. A test apparatus is used to make measurements of the pulsed light conductance of these devices having nominal gap spacings of 5, 10, 20 and 40 μm     

Type 2M von Willebrand disease: F606I and I662F mutations in the glycoprotein Ib binding domain selectively impair ristocetin- but not botrocetin-mediated binding of von Willebrand factor to platelets

von Willebrand disease (vWD) is a common, autosomally inherited, bleeding disorder caused by quantitative and/or qualitative deficiency of von Willebrand factor (vWF). We describe two families with a variant form of vWD where affected members of both families have borderline or low vWF antigen levels, normal vWF multimer patterns, disproportionately low ristocetin cofactor activity, and significant bleeding symptoms. Whereas ristocetin-induced binding of plasma vWF from affected members of both families to fixed platelets was reduced, botrocetin-induced platelet binding was normal. The sequencing of genomic DNA identified unique missense mutations in each family in the vWF exon 28. In Family A, a missense mutation at nucleotide 4105T --> A resulted in a Phe606Ile amino acid substitution (F606I) and in Family B, a missense mutation at nucleotide 4273A --> T resulted in an Ile662Phe amino acid substitution (I662F). Both mutations are within the large disulfide loop between Cys509 and Cys695 in the A1 domain that mediates vWF interaction with platelet glycoprotein Ib. Expression of recombinant vWF containing either F606I or I662F mutations resulted in mutant recombinant vWF with decreased ristocetin-induced platelet binding, but normal multimer structure, botrocetin-induced platelet binding, collagen binding, and binding to the conformation-sensitive monoclonal antibody, AvW-3. Both mutations are phenotypically distinct from the previously reported variant type 2MMilwaukee-1 because of the presence of normal botrocetin-induced platelet binding, collagen binding, and AvW-3 binding, as well as the greater frequency and intensity of clinical bleeding. When the reported type 2M mutations are mapped on the predicted three-dimensional structure of the A1 loop of vWF, the mutations cluster in one region that is distinct from the region in which the type 2B mutations cluster.     

Reduction of coal-water mixture consistency with soda ash and lime

The addition of soda ash and lime to improve the Theological properties of a 60 wt % bituminous coal-water mixture (CWM) was investigated. Soda ash and lime were used to precipitate calcium and magnesium cations naturally present in the aqueous phase of the CWM. Addition of the required amounts of soda ash and lime alone, based on analyses of the total Ca²⁺ and Mg²⁺ burdens in the CWM, using standard water softening technology as well as addition of soda ash and lime along with an ionic dispersant were studied. Significant reduction in consistency was measured following soda ash and lime addition alone, and marked reduction in consistency resulted when both soda ash and lime and dispersant were used. Additive costs to obtain a given degree of consistency reduction were lowered by factors ranging from 3 to 15 with soda ash and lime, either alone or in concert with an anionic dispersant, relative to the use of anionic dispersant alone.     

Detection in correlated impulsive noise using fourth-ordercumulants

We consider detection and estimation in correlated impulsive noise. The non-Gaussian impulsive noise is modeled as the sum of two linear processes: a nominal part and an impulsive part. This model admits correlated impulsive bursts lasting many data samples. Identifiability of the noise model is established using fourth- and second-order cumulants. Under this model, the correlated time series can be whitened and an appropriate memoryless nonlinearity applied to attenuate the impulsive events. A detection statistic is then formed from the output of the nonlinearity. In the threshold detection case, the use of cumulants allows identification of the noise in the presence of the signal to be detected, obviating the need for noise-only training records. Simulation results with a sample size of 512 show small loss in detector performance versus an ideal detector with no impulsive part present     

Blind reception of multicarrier DS-CDMA using antenna arrays

An asynchronous, multicarrier direct-sequence code-division multiple-access (DS-CDMA) array receiver is proposed based upon blind, composite channel vector estimation. Due to the fact that the combined effect of all received paths is estimated, the total number of paths can be greater than the number of antennas in the receiver array. Furthermore, the proposed approach is not limited by multipath coherency. The receiver is classified as an interference cancelling zero-forcing receiver, and multicarrier operation in a frequency-selective channel means that its performance can exceed that of a single-carrier array DS-CDMA. The effectiveness of the proposed approach, even in the presence of strong interference, is demonstrated by computer simulation studies.     

A 6.5-ns GaAs 20×20-b parallel multiplier with 67-ps gatedelay

The performance and yield of LSI circuits have been characterized over a wide variation in processing parameters and power supply voltage, and over the military temperature range using 4×4-, 8×8-, 12×12-, 16×16-, and 20×20-b multipliers. These parallel array multipliers with carry-save adder architecture have been implemented in low-power GaAs enhancement/depletion (E/D) direct-coupled FET logic (DCFL). The circuits were fabricated with a multifunction self-aligned gate process, which features a buried p-layer for high yield and manufacturability. Worst-case multiplication times ranging from 870 ps (51 ps/gate) for the 4×4-b, to 6.48 ns (67 ps/ gate) for the 20×20-b multiplier were obtained, with the fastest extracted gate delays yet reported for LSI circuits. The 20×20-b multiplier, with 18573 active devices (4902 logic gates), shows a wafer-probe yield as high as 61% on the best-yielding wafers. It is concluded that the E/D DCFL family is capable of providing LSI circuits operating over a wide variation in power-supply voltage and over the full military temperature range     

Morphometric study of the development of Purkinje cell dendritic trees in the mouse using vertex analysis

Vertices are the points in an arborescence which interconnect segments and comprise terminal or pendant vertices (Vp), nodal or branching points and the root point. Branching points may be dichotomous (Vd) or trichomtomous (Vt), etc., and are subdivided into distinct two-dimensional topological entities according to the number of terminal vertices they drain, i.e. Vds comprise primary vertices (Va), connecting two Vps; secondary vertices (Vb), connecting one Vp and one Vd or one Vt; and tertiary vertices (Vc), connecting either two Vds, two Vts or one Vt and one Vd. The four types of Vt (Va‘, Vb’, Vc‘, Vd’) similarly connect three, two, one and zero Vps respectively. Each Vt may be transformed into two Vds thus, Va' = Va + Vb; Vb’ = Va/3 + 4Vb/3 + Vc/3; Vc' = Vb + Vc and Vd’ = 2Vc. Analysis proceeds by transforming mixed trees containing varying proportions of Vds and Vts into entirely dichotomous branching structures. The topology is then defined by the Va Vb ratio which has a unique value according to the mode of growth and the frequency of Vts. Vertices are ordered by a centrifugal technique. The frequency distribution of vertices of different order allow the changes in growth characteristics and in remodelling to be detected within particular regions of the tree. Metrical parameters are readily incorporated into the analysis since all vertices are interconnected by segments of finite length and are given the same order magnitude as the vertex they drain. The analytical capabilities of the method are exemplified by its application to the study of growth and plasticity in the dendritic trees of Purkinje cells in the mouse. Growth is defined in metrical and topological terms and sites of reorganization within the mature tree are identified.