Deconstructing the Cosmological Constant

Deconstruction provides a novel way of dealing with the notoriously difficult ultraviolet problems of four-dimensional gravity. This approach also naturally leads to a new perspective on the holographic principle, tying it to the fundamental requirements of unitarity and diffeomorphism invariance, as well as to a new viewpoint on the cosmological constant problem. The numerical smallness of the cosmological constant is implied by a unique combination of holography and supersymmetry, opening a new window into the fundamental physics of the vacuum.Comment: Fourth Prize, 2003 Gravity Research Foundation Essay Contest; 7 pages, LaTe

Shear Thickening of Dense Suspensions: The Role of Friction

Shear thickening of particle suspensions is characterized by a transition between lubricated and frictional contacts between the particles. Using 3D numerical simulations, we study how the inter-particle friction coefficient influences the effective macroscopic friction coefficient and hence the microstructure and rheology of dense shear thickening suspensions. We propose expressions for effective friction coefficient in terms of distance to jamming for varying shear stresses and particle friction coefficient values. We find effective friction coefficient to be rather insensitive to interparticle friction, which is perhaps surprising but agrees with recent theory and experiments

Some Aspects on the Utility of Distance Measures in Comparing Two MROC Curves

Receiver Operating Characteristic (ROC) curve is a widely used and accepted tool to assess the performance of a classifier or procedure. Apart from this, comparing the procedures or ROC curves is also of interest. A multivariate extension of ROC (MROC) curve that considers a linear combination of several markers for classification was proposed by Sameera, Vishnu Vardhan and Sarma [13]. In the present paper, some inferential procedures are given to compare two MROC curves by means of distance measures based on scores of MROC curve and summary measures such as mean vectors and dispersion matrices. Real and Simulated data sets are used to demonstrate the above proposed inferential aspects

Regulation of Powder Mass Flow Rate in Gravity-Fed Powder Feeder Systems

Precise regulation of powder mass flow in laser-based manufacturing processes is critical to achieving excellent part dimensional and microstructure quality. Control of powder mass flow is challenging because low flow rates, where nonlinear effects are significant, are typically required. Also, gravity-fed powder feeder systems have significant material transport delays, making the control of powder mass flow even more challenging. This paper presents a control strategy for regulating the powder mass flow rate in a gravity-fed powder feeder system. A dynamic model of the powder feeder system, including material transport delay, is constructed, and a modified proportional plus integral (PI) controller is designed. An observer is used to estimate powder mass flow rate using the powder feeder motor encoder signal. The control strategy is implemented in a Smith Predictor Corrector Structure, which has been adjusted such that it can be applied to the modified PI controller, to account for the inherent material transport delay. Experimental studies are conducted that validate the dynamic model and controller strategy

Electronic-Structure Calculations of Cation-Ordered II-III Layered Double Hydroxides: Origin of the Distortion of the Metal-Coordination Symmetry

Cation ordering brings down the crystal symmetry and introduces distortion into the coordination polyhedra around the divalent cations. In particular, edge sharing of the differently sized M(OH)6 polyhedra causes a non-uniform distension of the array of hydroxy ions. The question arises as to whether this distortion has its origin in the Jahn�Teller distortion of metal coordination or a 2D �Peierls�-type distortion of the array of hydroxy ions. To address this question, DFT calculations were performed on the sulfate-intercalated Cu�Cr, Zn�Cr, and Zn�Al layered double hydroxides (LDHs). An analysis of the density of states shows that the distortion of the Cu2+ coordination polyhedron is due to the Jahn�Teller effect, whereas the Zn2+ coordination polyhedron in Zn�Al LDH likely suffers a �Peierls�-type distortion. In the Zn�Cr LDH, electronic-structure calculations do not predict any distortion in the metal coordination, which is in agreement with experimental results that show only a slight departure from ideal symmetry. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

AERODYNAMIC PERFORMANCE ANALYSIS OF CO-FLOW JET AIRFOIL

The work in this paper aims to increase the maximum lift coefficient of the airfoil by implementing the co-flow jet concept on NACA 0018 airfoil and also to investigate the performance of co-flow jet (CFJ) airfoil. To conduct numerical solution, RANS equations have been solved for 2D incompressible and unsteady flow using the Spalart-Allmaras turbulence model. The suction surface of the airfoil is modified by placing the injection slot near the leading edge and the suction slot near the trailing edge. A small mass of air is withdrawn into the airfoil suction slot, pressurized by a pumping system located inside the airfoil, and re-injecting into the injection slot tangentially to the main stream flow. The CFJ airfoil is enhancing the aerodynamic lift coefficient significantly compare to the baseline airfoil. And also, the numerical analysis is carried out to investigate the effect of the location of injection and suction slot. And it is observed that the aerodynamic lift coefficient of CFJ airfoil is increasing with varying the injection slot away from the leading edge

Detection of Compromised Accounts in Online Social Networks

Social behavioral profile appropriately reflects a user’s OSN activity patterns. People get right of entry to OSNs using both conventional computer PCs and new emerging cellular devices. With multiple billion customers global, OSNs are a brand new venue of innovation with many difficult studies issues. In this paper, we look at the social behaviors of OSN customers, i.e., their utilization of OSN offerings, and the utility of which in detecting the compromised accounts. We capture user conduct with the subsequent metrics: user connectivity, user hobby and user reactions. We validate and represent the person social hobby on OSN. The take a look at is based totally on distinct ClickStream data, the ClickStream data reveals key features of the social network workloads, consisting of how frequently humans connect to social networks and for a way lengthy, in addition to the kinds and sequences of activities that users conduct on those websites. We take note of the traits of social behaviors were view malicious behaviors of OSN users and show the social behavioral profiles can correctly differentiate man or woman OSN users and discover compromised account