Concurrent optimization strategies for high-performance VLSI circuits

In the next generation of VLSI circuits, concurrent optimizations will be essential to achieve the performance challenges. In this dissertation, we present techniques for combining traditional timing optimization techniques to achieve a superior performance;The method of buffer insertion is used in timing optimization to either increase the driving power of a path in a circuit, or to isolate large capacitive loads that lie on noncritical or less critical paths. The procedure of transistor sizing selects the sizes of transistors within a circuit to achieve a given timing specification. Traditional design techniques perform these two optimizations as independent steps during synthesis, even though they are intimately linked and performing them in alternating steps is liable to lead to suboptimal solutions. The first part of this thesis presents a new approach for unifying transistor sizing with buffer insertion. Our algorithm achieve from 5% to 49% area reduction compared with the results of a standard transistor sizing algorithm;The next part of the thesis deals with the problem of collapsing gates for technology mapping. Two new techniques are proposed. The first method, the odd-level transistor replacement (OTR) method, performs technology mapping without the restriction of a fixed library size, and maps a circuit to a virtual library of complex static CMOS gates. The second technique, the Static CMOS/PTL method, uses a mix of static CMOS and pass transistor logic (PTL) to realize the circuit, using the relation between PTL and binary decision diagrams. The methods are very efficient and can handle all ISCAS\u2785 benchmark circuits in minutes. On average, it was found that the OTR method gave 40%, and the Static/PTL gave 50% delay reductions over SIS, with substantial area savings;Finally, we extend the technology mapping work to interleave it with placement in a single optimization. Conventional methods that perform these steps separately will not be adequate for next-generation circuits. Our approach presents an integrated solution to this problem, and shows an average of 28.19%, and a maximum of 78.42% improvement in the delay over a method that performs the two optimizations in separate steps

Global SH-wave propagation in a 2D whole Moon model using the parallel hybrid PSM/FDM method

International audienceWe present numerical modeling of SH-wave propagation for the recently proposed whole Moon model and try to improve our understanding of lunar seismic wave propagation. We use a hybrid PSM/FDM method on staggered grids to solve the wave equations and implement the calculation on a parallel PC cluster to improve the computing efficiency. Features of global SH-wave propagation are firstly discussed for a 100-km shallow and 900-km deep moonquakes, respectively. Effects of frequency range and lateral variation of crust thickness are then investigated with various models. Our synthetic waveforms are finally compared with observed Apollo data to show the features of wave propagation that were produced by our model and those not reproduced by our models. Our numerical modeling show that the low-velocity upper crust plays significant role in the development of reverberating wave trains. Increasing frequency enhances the strength and duration of the reverberations. Surface multiples dominate wavefields for shallow event. Core-mantle reflections can be clearly identified for deep event at low frequency. The layered whole Moon model and the low-velocity upper crust produce the reverberating wave trains following each phases consistent with observation. However, more realistic Moon model should be considered in order to explain the strong and slow decay scattering between various phases shown on observation data

Vibro-acoustic coupled analysis excited by correlated turbulent boundary layer

Vibro-acoustic coupling is one of the most concerned problems in the design stage of aircraft and aerospace vehicle. An algorithm that integrates the finite element method (FEM), the boundary element method (BEM) and an acquisition method of excitation correlation is proposed to conduct the vibro-acoustic coupled analysis under correlated excitations in time and spatial domains. The Corcos/Smol’yakov-Tkachenko (ST) power spectral density models are adopted for the correlated excitation with a divisional method, and the vibro-acoustic coupled analysis of complex structures can be greatly simplified. First, a simply supported panel under correlated TBL is investigated to validate the proposed algorithm. Then, the proposed algorithm is applied to a stiffened panel to carry out the vibro-acoustic coupled analysis under three types of excitation: (a) perfectly correlated TBL, (b) partially correlated TBL based on the Corcos or ST model, and (c) uncorrelated TBL. Parameters which may affect the vibro-acoustic coupled analysis, such as the coupled effect, the correlation of excitation and the speed and thickness of the turbulence, are also discussed. Results show that the proposed method is suitable for the vibro-acoustic coupled analysis of complex systems under correlated random excitations. The vibro-acoustic coupling effect will result in a decrease in both the natural frequency and structural response under perfectly correlated excitation, and an increase in the structural response for partial correlated and uncorrelated excitations. However, the coupling effect has little influence on the acoustical response. The structural and acoustic responses due to partially correlated excitation are larger than that due to perfectly correlated excitation. Moreover, the structural and acoustic responses increase with the increment in turbulence speed and thickness, and the difference among the responses under the three different types of excitations rapidly increase with the increasing of the turbulence speed

Self-assembly of Zein-based microcarrier system for colon-targeted oral drug delivery

The advances in pharmaceutical technology allow for the development of various region-selective delivery systems for oral administration to optimize local and systemic therapy. In this paper, micronization associated with a polymorph modification approach was proposed for improving the solubility of hydrophobic drugs for developing a Zein-based colon-targeted delivery system. A microcarrier based on self-assembled structures of Zein was fabricated via a built-in ultrasonic dialysis process, which displayed high payload of a model drug, indomethacin (Indo), with its optimal crystal form. The possible self-assembly mechanism of Zein/Indo forming porous structure in the ultrasonic dialysis process was attributed to the results of intra- and/or intermolecular interactions between Zein and Indo. The designed microspheres, Zein-Indo@PDA, with a surface coating of polydopamine (PDA) not only rendered them enhanced stability and mechanical resistance but also hindered the premature drug release at undesired sites. This innovative formulation design may offer better chances of colon-targeted release

Observation of spin-orbit magnetoresistance in metallic thin films on magnetic insulators

A magnetoresistance effect induced by the Rashba spin-orbit interaction was predicted, but not yet observed, in bilayers consisting of normal metal and ferromagnetic insulator. Here, we present an experimental observation of this new type of spin-orbit magnetoresistance (SOMR) effect in a bilayer structure Cu[Pt]/Y3Fe5O12 (YIG), where the Cu/YIG interface is decorated with nanosize Pt islands. This new MR is apparently not caused by the bulk spin-orbit interaction because of the negligible spin-orbit interaction in Cu and the discontinuity of the Pt islands. This SOMR disappears when the Pt islands are absent or located away from the Cu/YIG interface, therefore we can unambiguously ascribe it to the Rashba spin-orbit interaction at the interface enhanced by the Pt decoration. The numerical Boltzmann simulations are consistent with the experimental SOMR results in the angular dependence of magnetic field and the Cu thickness dependence. Our finding demonstrates the realization of the spin manipulation by interface engineering.Comment: 12 pages, 4 figures, 14 pages in supplementary. To appear on Science Advance

ANALYSIS ON CONSTRUCTION DEFORMATION AND SUPPORTING STRUCTURE OF TWO-STEP AND THREESECTION EXCAVATION METHOD FOR SUPER LARGER SPAN HIGHWAY TUNNEL

The super larger span tunnel is a common form of highway reconstruction and expansionprojects in recent years. In order to determine the stability of tunnel structure of the two-step andthree-section excavation method of the III-level surrounding rock mass of the super larger spanhighway, the field test method was adopted. Relying on the Laohushan Tunnel in Jinan, Shandong,China, the deformation and the structure performance of the super larger span tunnel in III-levelsurrounding rock mass are analyzed, and the safety of the tunnel and the support structure isevaluated on this basis. The results show that the maximum settlement of the arch section of theGrade III surrounding rock section is 12.5mm, and the maximum clearance convergence is 5.8mm.Both of them are much smaller than the design reserved deformation of 80mm. The maximumpressure of the surrounding rock is 0.091MPa, showing that the force acting on the supportingstructure by surrounding rock mass is small. The inner and outer arched parts of the steel frameare subject to large stresses, and most of them are tensile stresses. The maximum stress of thesteel frame is 283 MPa, and occurs at the inner side of right arch waist. Although the local stressexceeds the yield strength of the steel (235 MPa), it does not exceed its ultimate compressivestrength of 400 MPa, and the tensile and compressive stress values of the other inner and outerparts do not exceed the yield strength. Mainly, the maximum stress appears on the left side wall,reaching 4.83 MPa, which is far less than the ultimate compressive strength of sprayed concrete(11.9 MPa). For super larger span highway tunnels, located in III-level surrounding rock mass,constructed by two-step and three-section excavation method, the initial support effectivelycontrolled the tunnel deformation, the supporting structures were fully protected and the tunnelstructure was stable. The super larger span tunnel is a common form in the road reconstructionand expansion project in recent years. In order to determine the stability of tunnel structure of thetwo steps and three excavation method of the III-level surrounding rock mass of the super largerspan highway, the field test method was adopted. Relying on the Laohushan Tunnel, thedeformation and the structure performance of the super larger span tunnel in III-level surroundingrock mass were analyzed. The results show that the maximum settlement of arch of the III-levelsurrounding rock mass is 12.5mm in super larger span highway tunnel, and the maximumclearance convergence is 5.8mm. Both of them are smaller than the design reserved deformationof 80mm. The maximum surrounding rock mass pressure is 0.091MPa, the force acting on thesupporting structure by surrounding rock mass are small. The inner and outer arched parts of the steel frame bear larger stress, and are mostly tensile stress. The maximum stress on inner side ofthe steel frame is 283 MPa, and occurs at the right arch waist. The maximum stress on the outerside of the steel frame is184 MPa, and occurs at the vault. The steel frame plays an important rolein the initial support, however the force does not reach the yield strength of the steel. The shotcreteis subjected to pressure, the maximum stress appears on the left side wall is 4.83 MPa, which ismuch smaller than the ultimate compressive strength of shotcrete of 25 MPa. So for super largerspan highway tunnels, located in III-level surrounding rock mass, constructed by two-step andthree-excavation method, the whole structure is stable

Past distribution of epiphyllous liverworts in China: The usability of historical data

Epiphyllous liverworts form a special group of bryophytes that primarily grow on the leaves of understory vascular plants in tropical and subtropical evergreen broadleaf forests. Being sensitive to moisture and temperature changes, epiphyllous liverworts are often considered to be good indicators of climate change and forest degradation. However, they are a poorly collected and taxonomically complicated group, with an only partly identified distribution pattern. In this study, we built four models based on 24 environmental variables at four different spatial resolutions (i.e., 1 km, 5 km, 10 km, and 15 km) to predict the past distribution of epiphyllous liverworts in China, using Maxent model and 63 historical location records (i.e., presence‐only data). Both area under the curve of the receiver operating characteristic (AUC) and true skill statistic (TSS) methods are used to assess the model performance. Results showed that the model with the predictors at a 15‐km resolution achieved the highest predictive accuracy (AUC=0.946; TSS=0.880), although there was no statistically significant difference between the four models (p > 0.05). The most significant environmental variables included aridity, annual precipitation, precipitation of wettest month, precipitation of wettest quarter, and precipitation of warmest quarter, annual mean NDVI, and minimum NDVI. The predicted suitable areas for epiphyllous liverworts were mainly located in the south of Yangtze River and seldom exceed 35°N, which were consistent with the museum and herbarium records, as well as the historical records in scientific literatures. Our study further demonstrated the value of historical data to ecological and evolutionary studies

Genomic characterization of ribitol teichoic acid synthesis in Staphylococcus aureus: genes, genomic organization and gene duplication

BACKGROUND: Staphylococcus aureus or MRSA (Methicillin Resistant S. aureus), is an acquired pathogen and the primary cause of nosocomial infections worldwide. In S. aureus, teichoic acid is an essential component of the cell wall, and its biosynthesis is not yet well characterized. Studies in Bacillus subtilis have discovered two different pathways of teichoic acid biosynthesis, in two strains W23 and 168 respectively, namely teichoic acid ribitol (tar) and teichoic acid glycerol (tag). The genes involved in these two pathways are also characterized, tarA, tarB, tarD, tarI, tarJ, tarK, tarL for the tar pathway, and tagA, tagB, tagD, tagE, tagF for the tag pathway. With the genome sequences of several MRSA strains: Mu50, MW2, N315, MRSA252, COL as well as methicillin susceptible strain MSSA476 available, a comparative genomic analysis was performed to characterize teichoic acid biosynthesis in these S. aureus strains. RESULTS: We identified all S. aureus tar and tag gene orthologs in the selected S. aureus strains which would contribute to teichoic acids sythesis.Based on our identification of genes orthologous to tarI, tarJ, tarL, which are specific to tar pathway in B. subtilis W23, we also concluded that tar is the major teichoic acid biogenesis pathway in S. aureus. Further analyses indicated that the S. aureus tar genes, different from the divergon organization in B. subtilis, are organized into several clusters in cis. Most interesting, compared with genes in B. subtilis tar pathway, the S. aureus tar specific genes (tarI,J,L) are duplicated in all six S. aureus genomes. CONCLUSION: In the S. aureus strains we analyzed, tar (teichoic acid ribitol) is the main teichoic acid biogenesis pathway. The tar genes are organized into several genomic groups in cis and the genes specific to tar (relative to tag): tarI, tarJ, tarL are duplicated. The genomic organization of the S. aureus tar pathway suggests their regulations are different when compared to B. subtilis tar or tag pathway, which are grouped in two operons in a divergon structure

Covering Radius of Two-dimensional Lattices

The covering radius problem in any dimension is not known to be solvable in nondeterministic polynomial time, but when in dimension two, we give a deterministic polynomial time algorithm by computing a reduced basis using Gauss\u27 algorithm in this paper

Evolution of Galaxy Luminosity Function and Luminosity Function by Density Environment at 0.03<z<0.5

Using galaxy sample observed by the BATC large-field multi-color sky survey and galaxy data of SDSS in the overlapped fields, we study the dependence of the restframe $r$-band galaxy luminosity function on redshift and on large-scale environment. The large-scale environment is defined by isodensity contour with density contrast \delta\rho/\rho. The data set is a composite sample of 69,671 galaxies with redshifts 0.03 < z < 0.5 and r < 21.5 mag. The redshifts are composed by three parts: 1) spectroscopic redshifts in SDSS for local and most luminous galaxies; 2) 20-color photometric redshifts derived from BATC and SDSS; 3) 5-color photometric redshifts in SDSS. We find that the faint-end slope \alpha steepens slightly from -1.21 at z ~ 0.06 to -1.35 at z ~ 0.4, which is the natural consequence of the hierarchical formation of galaxies. The luminosity function also differs with different environments. The value of \alpha changes from -1.21 at underdense regions to -1.37 at overdense regions and the corresponding M* brightens from -22.26 to -22.64. This suggests that the fraction of faint galaxies is larger in high density regions than in low density regions.Comment: 7 pages, 9 figures, accepted by Ap