Axial coordination and reduction potentials of the sixteen hemes in high-molecular-mass cytochrome c from Desulfovibrio vulgaris (Hildenborough)

A spectroelectrochemical study is described of the sixteen hemes in the high-molecular-mass, monomeric cytochrome c (Hmc) from the periplasmic space of Desulfovibrio vulgaris, strain Hildenborough. One of the hemes has special properties. In the oxidized state at pH 7 it is predominantly high-spin, S = 5/2, with a g perpendicular value of less than 6 indicative of quantum-mechanical mixing with a low-lying (800 cm-1) S = 3/2 state; the balance is probably a low-spin derivative. The high-spin heme has an Em.7.5 value of +61 mV. The fifteen other hemes are low-spin bis-histidine coordinated with Em.7.5 values of approximately -0.20 V. Two of these hemes exhibit very anisotropic EPR spectra with a g1 value of 3.65 characteristic for strained bis-histidine coordination. A previous proposal, namely that methionine is coordinated to one of the hemes [Pollock, W.B.R., Loufti, M. Bruschi, M. Rapp-Giles, B.J., Wall, J. & Voordouw, G. (1991) J. Bacteriol. 173, 220] is disproved using spectroscopic evidence. Contrasting electrochemical data sets from two previous studies [Tan, J. & Cowan, J.A. (1990) Biochemistry 29, 4886; Bruschi, M., Bertrand, P., More, C., Leroy, G., Bonicel, J., Haladjian, J., Chottard, G., Pollock, W.B.R. & Voordouw, G. (1992) Biochemistry 31, 3281] are not consistent with our EPR titration results and are not reproducible. Hmc can be reduced by D. vulgaris Fe-hydrogenase in the presence of molecular hydrogen.     

Interaction of Mycoplasma hyopneumoniae and Pasteurella multocida infections in swine

To investigate the interaction between Mycoplasma hyopneumoniae and Pasteurella multocida infection, 32 pigs were randomly assigned by litter, sex, and weight to 4 treatment groups. Group-1 pigs were inoculated with M hyopneumoniae and allowed to recover from M hyopneumoniae infection. Group-2 pigs were vaccinated against M hyopneumoniae and then inoculated with M hyopneumoniae. Group-3 pigs were inoculated with M hyopneumoniae and developed clinical signs of mycoplasmosis. Group-4 pigs had never been exposed to M hyopneumoniae. All pigs were initially seronegative for M hyopneumoniae. All pigs were subsequently inoculated with P multocida and euthanatized 2 weeks later. Pasteurella multocida was isolated only from the lungs of group-3 pigs, and these pigs had a significantly higher median percentage of lung surface area affected by pneumonia than did pigs in the other groups. For group-3 pigs, percentage of lung surface area affected by pneumonia was positively correlated with the number of P multocida colonies isolated. We concluded that P multocida is not a primary respiratory pathogen in pigs, but that M hyopneumoniae infection can render the lungs susceptible to P multocida colonization and infection. Pigs recovered from or vaccinated against infection with M hyopneumoniae were resistant to P multocida infection.     

Communication results for parallel sparse Cholesky factorization on a hypercube

We consider the problem of reducing data traffic among processor nodes during the parallel factorization of a sparse matrix on a hypercube multiprocessor. A task assignment strategy based on the structure of an elimination tree is presented. This assignment is aimed at achieving load balancing among the processors and also reducing the amount of processor-to-processor data communication. An analysis of regular grid problems is presented, providing a bound on communication volume generated by the new strategy, and showing that the allocation scheme is optimal in the asymptotic sense. Some experimental results on the performance of this scheme are presented.     

Effects of valve replacement on ventricular mechanics in mitral regurgitation and aortic stenosis

BACKGROUND: This study in humans assessed changes in left ventricular function early and late after correction of mitral regurgitation (MR) (n = 9) or aortic stenosis (AS) (n = 10). METHODS: Ventricular function was measured with radionuclide and micromanometer-derived pressure-volume loops during preload manipulation, thermodilution cardiac outputs, and echocardiograms. Late radionuclide and echocardiographic data were acquired at 24 hours and 20 months. RESULTS: Perioperative left ventricular performance (stroke work-end-diastolic volume relationship) did not change for patients with MR or AS. Significant changes in afterload occurred: ejection fraction (MR, 0.49 to 0.37; AS, 0.54 to 0.60; both, p = 0.013), mean left ventricular ejection pressure (MR, 73 to 91 mm Hg; AS, 138 to 93 mm Hg; both, p < 0.01), and end-systolic wall stress (MR, 26 to 42 x 10(3) dynes/cm2; AS, 37 to 22 x 10(3) dynes/cm2; both, p < 0.01). Ejection efficiency improved for MR patients (0.69 +/- 0.26 to 1.0 +/- 0.15; p < 0.05). The 20-month data showed improved New York Heart Association functional class, normal resting ejection fraction, and normal exercise response for both groups. CONCLUSIONS: Early after operation, a significant change in left ventricular load was seen with correction of MR and AS. Data obtained late after operation showed improvement consistent with ventricular remodeling.     

Irrelevant information in probabilistic categorization.

Using a probabilistic category learning paradigm, 6 experiments explored irrelevant information and 4 current models. Utilization of relevant configural information was lowered by the presence of an irrelevant dimension, both if that was the only relevant information and if a dimension was also relevant. An irrelevant cue value lowered the utilization of relevant cue values. An additional relevant dimension had a larger degrading effect on the utilization of a relevant dimension than an additional irrelevant dimension, thereby suggesting that the effect of irrelevant information is due to the complexity of the environment rather than to factors particular to the irrelevant nature of the information. The current models failed to fit the findings. However, results showing that memory errors account for salience effects provide a direction for revising one of the models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of AlxInyGa1−x−yN quaternary alloys grown on sapphire substrates by molecular-beam epitaxy

High-resolution X-ray diffraction (HR-XRD) with rocking curve, atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy have been performed on high-quality quaternary Al_xIn_yGa_1−x−yN thin films at room temperature. The Al_xIn_yGa_1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using a molecular beam epitaxy (MBE) technique with aluminum (Al) mole fractions x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. HR-XRD measurements confirmed the high crystalline quality of these alloys without any phase separation. The X-ray rocking curve of Al_xIn_yGa_1−x−yN films typically shows full widths at half maximum (FWHM) intensity between 14.4 and 28.8 arcmin. AFM measurements revealed a two-dimensional (2D) growth mode with a smooth surface morphology of quaternary epilayers. PL spectra exhibited both an enhancement of the integrated intensity and an increasing blueshift with increased Al content with reference to the ternary sample In_0.1Ga_0.90N. Both effects arise from Al-enhanced exciton localization. PL was used to determine the behavior of the energy band gap of the quaternary films, which was found to increase with increasing Al composition from 0.05 to 0.2. This trend is expected since the incorporation of Al increases the energy band gap of ternary In_0.1Ga_0.90N (3.004 eV). We have also investigated the bowing parameter for the variation of energy band gaps and found it to be very sensitive on the Al composition. A value of b=10.4 has been obtained for our quaternary Al_xIn_yGa_1−x−yN alloys.     

Throughput Analysis of IEEE802.11 Multi-Hop Ad Hoc Networks

In multi-hop ad hoc networks, stations may pump more traffic into the networks than can be supported, resulting in high packet-loss rate, re-routing instability and unfairness problems. This paper shows that controlling the offered load at the sources can eliminate these problems. To verify the simulation results, we set up a real 6-node multi-hop network. The experimental measurements confirm the existence of the optimal offered load. In addition, we provide an analysis to estimate the optimal offered load that maximizes the throughput of a multi-hop traffic flow. We believe this is a first paper in the literature to provide a quantitative analysis (as opposed to simulation) for the impact of hidden nodes and signal capture on sustainable throughput. The analysis is based on the observation that a large-scale 802.11 network with hidden nodes is a network in which the carrier-sensing capability breaks down partially. Its performance is therefore somewhere between that of a carrier-sensing network and that of an Aloha network. Indeed, our analytical closed-form solution has the appearance of the throughput equation of the Aloha network. Our approach allows one to identify whether the performance of an 802.11 network is hidden-node limited or spatial-reuse limited     

Board level solder joint reliability analysis of stacked die mixed flip-chip and wirebond BGA

Stacked die BGA has recently gained popularity in telecommunication applications. However, its board level solder joint reliability during the thermal cycling test is not as well-studied as common single die BGA. In this paper, solder joint fatigue of lead-free stacked die BGA with mixed flip-chip (FC) and wirebond (WB) interconnect is analyzed in detail. 3D fatigue model is established for stacked die BGA with considerations of detailed pad design, realistic shape of solder ball, and non-linear material properties. The fatigue model applied is based on a modified Darveaux’s approach with non-linear viscoplastic analysis of solder joints. Based on the FC–WB stack die configuration, the critical solder ball is observed located between the top and bottom dice corner, and failure interface is along the top solder/pad interface. The modeling predicted fatigue life is first correlated to the thermal cycling test results using modified correlation constants, curve-fitted from in-house lead-free TFBGA46 (thin-profile fine-pitch BGA) thermal cycling test data. Subsequently, design analyzes are performed to study the effects of 20 key design variations in package dimensions, material properties, and thermal cycling test conditions. In general, thinner PCB and mold compound, thicker substrate, larger top or bottom dice sizes, thicker top die, higher solder ball standoff, larger solder mask opening, smaller PCB pad size, smaller thermal cycling temperature range, longer ramp time, and shorter dwell time contribute to longer fatigue life. SnAgCu is a common lead-free solder, and it has much better board level reliability performance than eutectic solder based on modeling results, especially low stress packages.     

Cluster Based Routing Protocol for Mobile Nodes in Wireless Sensor Network

Mobility of sensor nodes in wireless sensor network (WSN) has posed new challenges particularly in packet delivery ratio and energy consumption. Some real applications impose combined environments of fixed and mobile sensor nodes in the same network, while others demand a complete mobile sensors environment. Packet loss that occurs due to mobility of the sensor nodes is one of the main challenges which comes in parallel with energy consumption. In this paper, we use cross layer design between medium access control (MAC) and network layers to overcome these challenges. Thus, a cluster based routing protocol for mobile sensor nodes (CBR-Mobile) is proposed. The CBR-Mobile is mobility and traffic adaptive protocol. The timeslots assigned to the mobile sensor nodes that had moved out of the cluster or have not data to send will be reassigned to incoming sensor nodes within the cluster region. The protocol introduces two simple databases to achieve the mobility and traffic adaptively. The proposed protocol sends data to cluster heads in an efficient manner based on received signal strength. In CBR-Mobile protocol, cluster based routing collaborates with hybrid MAC protocol to support mobility of sensor nodes. Schedule timeslots are used to send the data message while the contention timeslots are used to send join registration messages. The performance of proposed CBR-Mobile protocol is evaluated using MATLAB and was observed that the proposed protocol improves the packet delivery ratio, energy consumption, delay and fairness in mobility environment compared to LEACH-Mobile and AODV protocols.