2,787 research outputs found
Solving Multiple-Block Separable Convex Minimization Problems Using Two-Block Alternating Direction Method of Multipliers
In this paper, we consider solving multiple-block separable convex
minimization problems using alternating direction method of multipliers (ADMM).
Motivated by the fact that the existing convergence theory for ADMM is mostly
limited to the two-block case, we analyze in this paper, both theoretically and
numerically, a new strategy that first transforms a multi-block problem into an
equivalent two-block problem (either in the primal domain or in the dual
domain) and then solves it using the standard two-block ADMM. In particular, we
derive convergence results for this two-block ADMM approach to solve
multi-block separable convex minimization problems, including an improved
O(1/\epsilon) iteration complexity result. Moreover, we compare the numerical
efficiency of this approach with the standard multi-block ADMM on several
separable convex minimization problems which include basis pursuit, robust
principal component analysis and latent variable Gaussian graphical model
selection. The numerical results show that the multiple-block ADMM, although
lacks theoretical convergence guarantees, typically outperforms two-block
ADMMs
Renormalization group improved pQCD prediction for leptonic decay
The complete next-to-next-to-next-to-leading order short-distance and
bound-state QCD corrections to leptonic decay rate
has been finished by Beneke {\it et al.}
\cite{Beneke:2014qea}. Based on those improvements, we present a
renormalization group (RG) improved pQCD prediction for by applying the principle of maximum conformality (PMC). The PMC
is based on RG-invariance and is designed to solve the pQCD renormalization
scheme and scale ambiguities. After applying the PMC, all known-type of
-terms at all orders, which are controlled by the RG-equation, are
resummed to determine optimal renormalization scale for its strong running
coupling at each order. We then achieve a more convergent pQCD series, a
scheme- independent and more accurate pQCD prediction for
leptonic decay, i.e. keV, where the uncertainty is the squared average of
the mentioned pQCD errors. This RG-improved pQCD prediction agrees with the
experimental measurement within errors.Comment: 11 pages, 4 figures. Numerical results and discussions improved,
references updated, to be published in JHE
Quantum Nonlinear Effect in Dissipatively Coupled Optomechanical System
A full-quantum approach is used to study quantum nonlinear properties of a
compound Michelson-Sagnac interferometer optomechanical system. The effective
Hamiltonian shows that both dissipative and dispersive couplings possess
imaginary- and real-Kerr nonlinearities. And unexpectedly, the nonlinearities
caused by the dissipative coupling have non-Hermitian Hamiltonian-like
properties. It can protect the quantum nature of the dispersive coupling beyond
the traditional dissipation of the system. This protection mechanism allows the
system to exhibit strong quantum nonlinear effects in the parameter region of
the hyperbolic function . Moreover, we can obtain
strong anti-bunching effects whether in strong or weak coupling regimes with
the help of the dispersive and dissipative couplings jointly. It may provide a
new perspective to experimentally realize and study the strong quantum
nonlinear effects
Hydraulic fracturing propagation mechanism during shale gas reservoir stimulation through horizontal well
NaÄin razlamanja stijenske mase u naslagama naftnih Å”kriljaca jedan je od glavnih Äimbenika koji djeluju na uÄinkovitost hidrauliÄkog frakturiranja (frakiranja). U ovom su radu provedena fizikalna ispitivanja i numeriÄko modeliranje u svrhu sustavnog ispitivanja uÄinka in-situ (podzemnog) naprezanja i kuta buÅ”enja na stvaranje tlaka zbog hidrauliÄkog frakturiranja, Å”irenje razlamanja i naÄin razlamanja u horizontalnoj buÅ”otini naftnog nalaziÅ”ta Shengli u Luojia pokrajini, u izvoÄenju Sinopec Corp. Ukupno je razmatrano Å”est razliÄitih in-situ kombinacija naprezanja i osam razliÄitih kutova buÅ”enja slojevite stijenske mase tijekom hidrauliÄkog frakturiranja. Sažetak nastanka i Å”irenja pukotine te zavrÅ”ni oblici pukotina nastalih hidrauliÄkim frakturiranjem u slojevitim stijenskim masama otkrivaju da kod stratificiranih stijena s istim kutom buÅ”enja, Å”to je veÄi in-situ omjer naprezanja (t.j. niže maksimalno horizontalno osnovno naprezanje pri konstantnim vertikalnim naprezanjem), potreban je niži hidrauliÄki tlak za poticanje i Å”irenje hidrauliÄkog frakturiranja. Å toviÅ”e, ustanovljeno je da je kod stratificirane stijenske mase pri istom omjeru naprezanja, tlak hidrauliÄkog frakturiranja, u sluÄaju kad je kut buÅ”enja 30Ā°, veÄi nego u svim drugim sluÄajevima. Nadalje, zapaženo je da uÄinak stratifikacije na hidrauliÄko frakturiranje postaje slabiji s porastom in-situ omjera naprezanja. KonaÄno je zakljuÄeno da rezultati ove analize mogu biti važan teorijski pokazatelj u poboljÅ”anju oblikovanja hidrauliÄkog frakturiranja kako bi se osiguralo uÄinkovito stimuliranje naslaga naftnih Å”kriljaca.The fracture pattern of rock mass in shale gas reservoirs is one of the main factors affecting the efficiency of hydraulic fracturing. In this paper, physical experiments and numerical modelling were conducted to systematically investigate the effect of the in-situ stress and perforation angle on the hydraulic fracture initiation pressure and location, fracture propagation, and fracture pattern in a horizontal well drilled by Sinopec Corp. in Luojia area of Shengli Oilfield. A total of six different in-situ stress combinations and eight different perforation angles were considered for the stratified rock mass during the hydraulic fracturing. A summary of the fracture initiations and propagation, and the final fracture patterns induced by the hydraulic fracturing in the stratified rock masses reveals that, for the stratified rock masses with the same perforation angle, the larger the in-situ stress ratio (i.e. lower maximum horizontal principal stress when the vertical stress remains constant) is, the lower hydraulic pressure is required for hydraulic fracturing initiation and propagation. Moreover, it is found that, for the stratified rock mass under the same stress ratio, the hydraulic fracturing pressure in the case with a perforation angle of 30Ā° is higher than that in all other cases. Furthermore, it is noted that the effect of the stratification on the hydraulic fracturing becomes weaker with the in-situ stress ratio increasing. It is finally concluded that the results from this study can provide important theoretical guidance for improving the hydraulic fracturing design in order to ensure the effective shale gas reservoir stimulations
Fully integrated InGaAs/InP single-photon detector module with gigahertz sine wave gating
InGaAs/InP single-photon avalanche diodes (SPADs) working in the regime of
GHz clock rates are crucial components for the high-speed quantum key
distribution (QKD). We have developed for the first time a compact, stable and
user-friendly tabletop InGaAs/InP single-photon detector system operating at a
1.25 GHz gate rate that fully integrates functions for controlling and
optimizing SPAD performance. We characterize the key parameters of the detector
system and test the long-term stability of the system for continuous operation
of 75 hours. The detector system can substantially enhance QKD performance and
our present work paves the way for practical high-speed QKD applications.Comment: 11 pages, 6 figures. Accepted for publication in Review of Scientific
Instrument
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