Top Configuration Research Articles

Automatic Cloud I/O Configurator for I/O Intensive Parallel Applications

As the cloud platform becomes a promising alternative to traditional HPC (high performance computing) centers or in-house clusters, the I/O bottleneck problem is highlighted in this new environment, typically with top-of-the-line compute instances but sub-par communication and I/O facilities. It has been observed that changing the cloud I/O system configurations, such as choices of file systems, number of I/O servers and their placement strategies, etc., will lead to a considerable variation in the performance and cost efficiency of I/O intensive parallel applications. However, storage system configuration is tedious and error-prone to do manually, even for expert users, leading to solutions that are grossly over-provisioned (low cost inefficiency), substantially under-performing (poor performance) or, in the worst case, both. This paper proposes ACIC, a system which automatically searches for optimized I/O system configurations from many candidates for each individual application running on a given cloud platform. ACIC takes advantage of machine learning models to perform performance/cost predictions. To tackle the high-dimensional parameter exploration space, we enable affordable, reusable, and incremental training on cloud platforms, guided by the Plackett and Burman Matrices for experiment design. Our evaluation results with four representative parallel applications indicate that ACIC consistently identifies optimal or near-optimal configurations among a large group of candidate settings. The top ACIC-recommended configuration is capable of improving the applications’ performance by a factor of up to 10.5 (3.1 on average), and cost saving of up to 89 percent (51 percent on average), compared with a commonly used baseline I/O configuration. In addition, we carried out a small-scale user study for one of the test applications, which found that ACIC consistently beat the user and even the application’s developer, often by a significant margin, in selecting optimized configurations.

Effect of baffle number on mixed convection within a ventilated cavity

Transverse mixed convection is studied numerically in a ventilated cavity with uniform heat flux on the bottom wall and the remaining walls are adiabatic. Our purpose was to see the influence of the baffle number on the variation of average Nusselt number. An air flow inlet in to the cavity through an opening in the lower part of the left vertical wall and another opening in the opposite wall (i.e., the bottom part BB configuration; the top part BT configuration). The number of baffles ranged between 1 and 4. The two-dimensional mathematical model includes a system of four equations with partial derivatives of continuity, momentum, and energy, solved by the finite volume method. Flow fields are studied by numerical simulations to the air with a Richardson number in the range1≤ Ri ≤10, for the Grashof number is fixed atGr =104, aspect ratio of the cavity A = 2, the height openings w = 0.1 and Prandtl number Pr = 0.71. The results show that the variation of the average Nusselt number and the average temperature depend on the type of configuration (BB or BT), and of the baffle number. The basic nature of the resulting interaction between the forced external air stream and the buoyancy-driven flow by the heat source is explained by the Nusselt number and the patterns of the streamlines and isotherms.

The Electronic Structure and Bonding of Acetylene on PdGa(110)

We have studied the adsorption of acetylene on the PdGa(110) surface by Density Functional Theory calculation. Our results predict the hollow site is the most stable location for the adsorbate. In this site, both Pd and Ga atoms interact with acetylene. This molecule is bonded with the C–C bond almost parallel to the surface. A small tilt angle of 4.1° is computed. The C atoms present a rehybridization from sp → sp2. This rehybridization is also present in the bridge site but it is not present in the top configuration, where the C–C–H bond angle is about 160°. We computed the total density of state for the system and also the projection on Pd, Ga, C, and H atoms. These plots show a shift to lower energies on C and H projected states, which is an indication of stabilization after adsorption. At the same time, there is a reduction in the density for the Pd atom directly bonded to the C atom. The crystal orbital overlap population curves show an increase in the C–C overlap population (OP) after adsorption; while, the C2H2 rehybridizes to a near sp2 geometry. The acetylene withdraws charge from the surface indicating a donation–adsorption mechanism. The formation of Pd–C and Ga–C bonds and a decrease in OP for Pd–Pd and Pd–Ga bonds are detected. We also found, in the hollow site, a reduction in the C–C bond stretching vibrational frequency. This is an indication of the significant distortion in the adsorbed molecule. We have also found that the C–C bond breaking is unfavorable and that semihydrogenation is 2.27 eV more stable than C2H2 + H2 in the gas phase.

Design, fabrication and performance evaluation of solar dryer for banana

An indirect, active-type, environmentally friendly, low-cost solar dryer was designed to dry various agricultural products. The dryer was built by locally available, biologically degradable, low-cost materials. The dryer consists of solar flat plate air heater with three layers of insulation, drying chamber and a fan with a regulator to induce required air flow in the system. Banana is the chosen crop for the experimentation since it is high in production and also has substantial loss in India. Also, dried bananas are having good nutritive value which makes it as essential diet. The experiments were conducted to dry banana slices and to study its drying characteristics like rate of drying and quality of dried banana in terms of taste, colour and shape. The dryer has the following features: two different air flow configurations (air flow between glass cover and absorber plate called as the top flow and air flow between absorber plate and the bottom insulation of solar collector called as the bottom flow), forced flow with variable flow rates from 0–3 m/s and two different mounting schemes (conventional trays and wooden skewers). In the top and bottom flow experiments, the bottom flow provided about 2.5 °C higher chamber temperatures than the top flow for the same solar energy input. The efficiency of top flow configuration was found to be 27.5 %, whereas the efficiency of bottom flow configuration was found to be higher at 38.21 %. The results also agree well with the theoretical calculations performed as 60 W of energy can be saved for the same energy input. The drying rate was found to increase when wooden skewers were used instead of conventional trays. At the end of the day, the total difference in moisture content is found to be 3.1 % which is considerable knowing that the rate of drying drastically decreases with time. Banana dried at 1 m/s air flow rate was of the best quality in terms of colour, taste and shape when compared to drying at 0.5 and 2 m/s air flow rate while the weather condition and ambient conditions were almost the same for all the cases with negligible difference.

Density Functional Theory Study on the Carbon-Adhering Reaction on Fe3O4(111) Surface

The density functional theory (DFT) has been employed to investigate the carbon-adhering reaction on Fe3O4(111) surface, which consists of two steps: (1) the adsorption of CO onto the Fe3O4(111) surface and (2) the second CO seizes an O atom from CO, which adsorbed on the surface, to form a CO2 molecule and the C atom left behind adheres onto the Fe3O4(111) surface. At step 1, there are five stable configurations of CO adsorbed onto Feoct2-terminated Fe3O4(111) surface and four stable formations of CO adsorbed onto the Fetet1-terminated Fe3O4(111) surface. The top configurations of these two surfaces are most stable. Moreover, a density of the state (DOS) analysis is used to investigate the bonding mechanism of CO adsorbed onto these two surfaces. The results reveal the new C-O bonds generation on two surfaces, which is important and necessary for the formation of a CO2 molecule. Besides, the transition states (TS) are searched to analyze the energy barrier in the process of CO2 desorption from two surfaces. The result indicates that the oxidation reaction of adsorbed CO molecule and surface O atom is feasible. For step 2, the result shows that the carbon-adhering reaction occurs only on the top site of Feoct2 atom and the magnetite plays a catalytic role in the carbon-adhering reaction process.

Theory for STM images of resonances in the near-field regime: application to adsorbates and local defects on graphene

We analyze the STM current through electronic resonances on a substrate as a function of tip-surface distance. We show that when the tip approaches the surface a maximum of the density of states of the electronic resonance at some energy can lead to a dip of the STM signal dI/dV. This phenomenon is a Fano effect resulting from the coupling of the electronic states of the STM tip with the resonance. In graphene such resonances can be produced by local defects or adsorbates and we analyze the cases of top and hollow configurations of adsorbates.

Top Management Team Configuration and Strategic Resource Reallocation

The top management team (TMT) plays an important role in determining how resources will be allocated among the business units of the firm. However, firms tend to maintain spending levels in each of...

Hydromagnetic Stability of Al2O3-Water and CuO-Water Nanofluids: Effect on Critical Rayleigh Number

In the present paper, hydromagnetic stability of alumina-water and copper oxide-water nanofluids is investigated for top heavy configuration of nanoparticles. Brownian motion and thermophoretic forces are introduced due to the presence of nanoparticles and Lorentz force term is added in the momentum equation due to the presence of magnetic field. The problem has application in geophysics due to earth's magnetic field and enhanced heat transfer characteristics of nanofluids. Computations are carried out within the frame work of normal mode technique and single term Galerkin approximation. An eigen value equation representing the relation between various nanofluid parameters, magnetic field, growth rate of disturbance and wave number is obtained. It is observed that the thermal Rayleigh number increases with the increase in Chandrasekhar number and decreases with the increase in volume fraction of nanoparticles. Nanofluids with Al2O3 nanoparticles exhibit higher stability than the nanofluids containing CuO nanoparticles. The mode of instability is found to be through stationary convection. It is expected since for oscillatory motions to exist two of the buoyancy forces must act in the opposite directions.

Core–shell InGaN/GaN nanowire light emitting diodes analyzed by electron beam induced current microscopy and cathodoluminescence mapping

We report on the electron beam induced current (EBIC) microscopy and cathodoluminescence (CL) characterization correlated with compositional analysis of light emitting diodes based on core/shell InGaN/GaN nanowire arrays. The EBIC mapping of cleaved fully operational devices allows to probe the electrical properties of the active region with a nanoscale resolution. In particular, the electrical activity of the p-n junction on the m-planes and on the semi-polar planes of individual nanowires is assessed in top view and cross-sectional geometries. The EBIC maps combined with CL characterization demonstrate the impact of the compositional gradients along the wire axis on the electrical and optical signals: the reduction of the EBIC signal toward the nanowire top is accompanied by an increase of the CL intensity. This effect is interpreted as a consequence of the In and Al gradients in the quantum well and in the electron blocking layer, which influence the carrier extraction efficiency. The interface between the nanowire core and the radially grown layer is shown to produce in some cases a transitory EBIC signal. This observation is explained by the presence of charged traps at this interface, which can be saturated by electron irradiation.

Low Temperature Gas Sensing with Novel Top-bottom Electrode Configuration

Gas sensors based on undoped and Cr doped TiO2 layers with novel top and bottom electrode (TBE) configuration have been employed for NO2 and H2 gas sensing. The sensing layers of about 2 micro-meter thickness were sandwiched between 200nm thick Pt top and bottom electrodes. These sensors with TBE configuration show promising gas sensing behaviour towards both oxidizing and reducing gases. The crystal structure, microstructure and chemical composition studies of the sensors were performed by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. The comparative structural, morphological and compositional studies enable us to understand the effect of Cr3+ (0.755Å) substitution within Ti4+ (0.745Å) lattice on gas sensing properties (24°-200°C). The Cr doped TiO2 sensors were able to detect various concentrations of NO2 at 200°C and H2 at room temperature. Response/recovery times are in the order of tens of seconds for NO2 at 200°C and a few minutes for H2 at room temperature.

Optimization of thin noise barrier designs using Evolutionary Algorithms and a Dual BEM Formulation

This work aims at assessing the acoustic efficiency of different thin noise barrier models. These designs frequently feature complex profiles and their implementation in shape optimization processes may not always be easy in terms of determining their topological feasibility. A methodology to conduct both overall shape and top edge optimizations of thin cross section acoustic barriers by idealizing them as profiles with null boundary thickness is proposed. This procedure is based on the maximization of the insertion loss of candidate profiles proposed by an evolutionary algorithm. The special nature of these sorts of barriers makes necessary the implementation of a complementary formulation to the classical Boundary Element Method (BEM). Numerical simulations of the barriers׳ performance are conducted by using a 2D Dual BEM code in eight different barrier configurations (covering overall shaped and top edge configurations; spline curved and polynomial shaped based designs; rigid and noise absorbing boundaries materials). While results are achieved by using a specific receivers' scheme, the influence of the receivers' location on the acoustic performance is previously addressed. With the purpose of testing the methodology here presented, a numerical model validation on the basis of experimental results from a scale model test [34] is conducted. Results obtained show the usefulness of representing complex thin barrier configurations as null boundary thickness-like models.

The role of metal contacts in the stability of n-type organic field effect transistors

We are presenting a long-time bias stress stability of C60-based n-type organic field effect transistors (OFETs), in bottom gate, top contacts configuration, with aluminium (Al), silver (Ag) and gold (Au) source–drain contacts. The results clearly shows that the bias stress effects in C60-based n-type OFETs is similar to p-type OFETs and it can be reduced by using an appropriate metal for the source–drain contacts. During the bias stress time, the threshold voltage shift and an increase in the contacts resistance have also been measured. On the basis of the stability of the device parameters, it is proposed that the Al source–drain contact-based devices gives better stability as compared to the devices with Ag and Au source–drain contacts. Our results show that the bias stress-induced threshold voltage shift is due to the trapping of charges in the channel region and in the vicinity of the source–drain contacts.

Radial Epitaxy of Silicon for Optoelectronic Applications

At the heart of the dramatic transition in semiconductor device technology from planar to three-dimensional (3D) architectures is the ability to shrink devices to nanoscale dimensions with near atomic level control of materials’ structure and composition. The 3D structures serve as building blocks for high-performance electronic and photonic devices such as photovoltaic cells, light-emitting diodes, multi-gate field effect transistors and require unprecedented control in dimensions and materials properties. Epitaxial crystal growth, along with lithographic and etching technologies, provides one of the enabling approaches to create such structures. The standard for epitaxy in electronics technology is chemical vapor deposition (CVD) growth, which enables preparation of 3D semiconducting nanomaterials with modulated composition and electrical dopant profiles, with silicon (Si) epitaxy being arguably the world’s best studied crystal growth system. It is thus important to understand Si epitaxy on nanoscale structures, since any change in crystal growth kinetics at small sizes would have a large effect on dimensional control from a technological perspective and would also be of great interest from a fundamental perspective for understanding atomic scale processes and fabricating novel structures. We show that Si epitaxial growth at the nanoscale becomes size dependent at dimensions significantly larger than the onset of thermodynamic limits, and that this previously unknown behavior within the mesoscopic size regime for one of the best known crystal growth systems is a general phenomenon. A monotonic reduction in homoepitaxial growth rate with size is observed for facet widths below certain scale and the results modeled by an area-dependent precursor incorporation rate. The presence of n and p type dopants results in even greater reductions in low temperature radial growth rates, and a critical thicknesses for Si single crystal radial epitaxy is found for phosphorus. The results provide new insights on the nature of CVD crystal growth at small dimensions and have significant implications for 3D nanoscale fabrication of technologically important Si electronic device architectures. Si radial p-i-n junction nanowire structure is a suitable platform to integrate fundamental understanding and applications since the structure provides an approach for realizing concurrent maximization of light absorption and photogenerated carrier separation in photovoltaic (PV) devices. Additionally, NW arrays embedding radial p-(i)-n junctions enhance light absorption significantly in wide range of wavelengths. Si radial p-i-n junctions consisted of core Si NWs and Si shells. Core Si NWs were prepared by top-down consisting of lithographic technique and deep reactive ion etching. After formation of Si NWs, the color of Si substrate in NW regions turned to be black from shiny metallic surface. The change of color indicates enhanced light absorption in visible wavelengths. Electrically doped Si radial shell was prepared by epitaxial growth on the surfaces of Si NWs via low-pressure chemical vapor deposition. PV characteristics of crystalline Si radial p-i-n junction arrays prepared by top-down approach and epitaxial shell growth were investigated by current–voltage measurements under dark and Air Mass 1.5G conditions. Though the unoptimal dimensions of NWs and top electrode configuration, the open circuit voltage, short circuit current density, and photoconversion efficiency of the device were 0.46 V, 40 mA/cm2, and 10%, respectively. The high short circuit current density comparable to that of commercialized Si PV cell indicates that efficient photogenerated generation/collection is occurred in Si radial p-i-n junction.

Laser-induced forward transfer of multi-layered structures for OTFT applications

We report on the one-step laser printing of multi-layered organic-based field effect transistors, using thin films of bis(2-phenylethynyl) end-substituted terthiophene (diPhAc-3T) as semiconductor, parylene-C (Py-C) as dielectric and silver (Ag) as gate electrode, respectively. The laser-induced forward transfer (LIFT) process was used to transfer pixels from donor to receiver substrates. The latter included pre-designed source and drain gold electrodes to form complete organic thin films transistors (OTFTs). Such laser-induced forward transfer used a single 50ps duration pulse delivered by a Nd:YAG laser operating at 355nm to print transistor pixel arrays under ambient temperature. The pixels (350μm sized-squares, and 700±40nm in thickness), fabricated in the top gate configuration, were investigated for their current–voltage characteristics immediately after printing. Electrical characterization demonstrated that the laser printed transistor is fully functional with hole mobilities of 4×10−4cm2/Vs, a threshold voltage Vt near −10V, Ion/Ioff ratio near to 104–105 and the sub-threshold slope (S) of 14–18V/decade. The efficient cohesion between the three different layers composing the pixels offers an exceptionally high strength to laser printing, while maintaining the electrical properties.

Conteo de personas con un sensor RGBD comercial

In this paper, we prove that depth information provided by a consumer depth camera is a reliable data source to perform ro- bust people counting. The adoption of a top view configuration reduces the space problem complexity for this task, while pre- serving privacy. Two different background subtraction approaches for color images are transferred to this context and tested in real video to perform detection, tracking, and behavioral pat- terns analysis of subjects crossing the field of view. The results achieved in an experimental setup with real video reported a TPR over 95%, beating robust GMM background subtraction based only on the visual cue. The results suggest the benefits of the depth cue for this particular task.

Impacts of inlet–outlet configuration, flow rate and filter size on hydraulic behavior of quasi-2-dimensional horizontal constructed wetland: NaCl and dye tracer test

The aim of this study was to assess the influences of filter size, inflow rate and inlet–outlet configuration on short-circuiting, effective volume, distribution of active/dead zones, dispersion and dye propagation in simulated constructed wetlands. A subsurface quasi two dimensional flow constructed wetland was set up for chloride tracer test and dye visualization. Three levels of filter size, inflow rate and inlet–outlet configurations were involved. Totally 81 combinations were determined. Breakthrough curves for residence time distribution and images for dye tracer propagation were obtained. Results showed that the inflow rate and inlet–outlet configurations had significant effects on hydraulic behavior. Bigger filter size and low influent decreased short-circuiting and reduced dead zones, thus increasing active area. Bigger filter size enhanced plug flow by decreasing porous water velocity, reducing preferential flow. High flow rate yielded low plug flow with lower CSTRs number caused by higher linear velocities and enlarged dispersion. Inlet–outlet configuration had most influences on flow distribution. Inflow rate had larger impacts on dead zones distribution for low inlet–high outlet configuration. For practical constructed wetland design, choice of inlet–outlet configuration and inflow rate would improve the treatment efficiency. Larger porous size, lower inflow rate with bottom inlet–top outlet configuration could help improve hydraulic behavior, thus enhancing wastewater treatment.

On the electrochemical properties of platinum stepped surfaces vicinal to the (100) pole. A computational study

DFT studies on platinum stepped surfaces have been carried out in order to understand the differences in the electrochemical behavior between the surfaces with (111) and (100) terraces. Thus, adsorption energies of different species on selected surfaces have been computed. For the adsorption of Bi and Cu on the Pt(553) and Pt(711) surfaces, it has been found that the adsorption energy on the site corresponding to the step decoration for the Pt(553) surface is ca. 0.5eV higher than that calculated on the (111) terrace sites. On the other hand, there is no preferential adsorption site for Cu or Bi on the Pt(711) surface, since the energy differences between the different sites on this stepped surface with (100) terraces are very small. CO and OH adsorption on the surfaces with (100) terraces, namely the Pt(100), the Pt(711) and the Pt(510) surfaces, has been also investigated. The energy differences between step sites and terrace sites for the surfaces are very small, ca. 0.2eV for OH adsorption and <0.1eV for CO adsorption. For OH, the preferred adsorption mode is a bridge mode, whereas the adsorption energy for the on top and bridge configurations of CO are similar on those surfaces. The comparison with previous DFT calculations indicates that the perturbation created by the step on the (100) terrace is significantly smaller than that created on the (111) terraces. Thus, the modification of the electrochemical properties produced by the presence of a step in the (100) terrace is minor, in agreement with the experimental results.

High Coverage CO Activation Mechanisms on Fe(100) from Computations

CO activation on Fe(100) at different coverage was systematically computed on the basis of spin-polarized density functional theory. At the saturated coverage (11CO) on a p(3 × 4) surface size (24 exposed Fe atoms), top (1CO), bridge (3CO) and 4-fold hollow (7CO) adsorption configurations coexist. The stepwise adsorption energies and dissociation barriers at different coverage reveal equilibriums between desorption and dissociation of adsorbed CO molecules. It is found that only molecular adsorption is likely for nCO = 8–11, and mixed molecular and dissociative adsorption becomes possible for nCO = 5–7, while only dissociative adsorption is favorable for nCO = 1–4. The computed CO adsorption configurations and stretching frequencies as well as desorption temperatures from ab initio thermodynamic analysis agree well with the available experimental data.

Optical control of large-signal properties of millimeter-wave and sub-millimeter-wave DDR Si IMPATTs

The authors have proposed a complete large-signal (L-S) model to investigate the optical modulation of high frequency properties of double-drift region (DDR) impact avalanche transit time (IMPATT) devices operating at different millimeter-wave and sub-millimeter-wave frequencies. Simulation is carried out based on the proposed model to study the effect of photo-irradiation of different values of incident optical power of different wavelengths from 600---1000 nm on the DC and L-S characteristics of DDR IMPATTs based on Si designed to operate at 94, 140, 220, 300 and 500 GHz. Two different optical illumination configurations such as top mount and flip chip are taken into account for the present study. Results show that the maximum optical tuning of L-S parameters of the device can be achieved for optical illumination of wavelength 700 nm, i.e. near the wavelength corresponding to the responsivity peak of Si in both top mount and flip chip configurations. Further, better photo-sensitivity of top mount structure is observed as compared to its flip chip counterpart. The simulation results are found to be in good agreement with the experimental results reported earlier. Suitable tunable light source information is also suggested to carry out the optical control experiment within the wavelength range under consideration.

Effects of the structure of charged impurities and dielectric environment on conductivity of graphene

We investigate the conductivity of doped graphene in the semiclassical Boltzmann limit, as well as the conductivity minimum within the self-consistent transport theory. Using the hard-disk model for a two-dimensional distribution of impurities gives rise to both strong increase in the slope of conductivity at low charge carrier densities in graphene and a strongly sub-linear behavior of the conductivity at high charge carrier densities when the correlation distance between the impurities is large. On the other hand, we find that a super-linear dependence of the conductivity on charge carrier density in heavily doped graphene may arise from increasing the distance of impurities from graphene or allowing their clustering, whereas the existence of a electric dipole impurities may give rise to an electron-hole asymmetry in the conductivity. We show that finite thickness of a dielectric layer in the top gating configuration, as well as the existence of non-zero air gap(s) between graphene and the dielectric(s) exert strong influences on the conductivity and its minimum. While a decrease in the dielectric thickness is shown to increase the conductivity in doped graphene and even gives rise to finite conductivity in neutral graphene for a 2D distribution of impurities. We find that an increase in the dielectric thickness gives rise to a super-linear behavior of the conductivity when impurities are homogeneously distributed throughout the dielectric. Moreover, the dependence of graphene's mobility on its charge carrier density is surprisingly strongly affected, quantitatively and qualitatively, by the graphene-dielectric gap(s) when combined with the precise position of a 2D distribution of charged impurities. Finally, we show the changes in the conductivity minimum in neutral graphene as the correlation distance between the impurities and the dielectric thickness is altered.