Diffusion Monte Carlo: Exponential scaling of computational cost for large systems

The computational cost of a Monte Carlo algorithm can only be meaningfully discussed when taking into account the magnitude of the resulting statistical error. Aiming for a fixed error per particle, we study the scaling behavior of the diffusion Monte Carlo method for large quantum systems. We identify the correlation within the population of walkers as the dominant scaling factor for large systems. While this factor is negligible for small and medium sized systems that are typically studied, it ultimately shows exponential scaling. The scaling factor can be estimated straightforwardly for each specific system and we find that is typically only becomes relevant for systems containing more than several hundred atoms.Comment: 6 pages, 3 figures, published by Phys. Rev. B (further changes following referee's reports

Hybrid Codes

A hybrid code can simultaneously encode classical and quantum information into quantum digits such that the information is protected against errors when transmitted through a quantum channel. It is shown that a hybrid code has the remarkable feature that it can detect more errors than a comparable quantum code that is able to encode the classical and quantum information. Weight enumerators are introduced for hybrid codes that allow to characterize the minimum distance of hybrid codes. Surprisingly, the weight enumerators for hybrid codes do not obey the usual MacWilliams identity.Comment: 5 page

Hodnotenie kvality povrchu vozovky v cestnom tuneli

The paper discusses a method for quantitative evaluation of the road surface based on processing of the cloud of 3D points. The points are measured by high-speed laser scanner mounted on the vehicle. Such approach allows to scan the road surface without the need to stop the traffic inside the tunnel. The obtained data are processed in offline mode. The processing algorithm evaluates the structure (texture) of the surface, which has the direct impact on the safety of the road transport.Článok sa zaoberá metódou kvalitatívneho hodnotenia povrchu vozovky, založenou na spracovaní mračna 3D bodov. Body sú získané meraním pomocou vysokorýchlostného laserového skenera namontovaného priamo na vozidle. Tento prístup umožňuje skenovanie povrchu vozovky bez nutnosti zastaviť premávku v tuneli. Získané dáta sú spracovávané off-line. Algoritmus spracovania dát hodnotí štruktúru (textúru) povrchu vozovky, ktorá má priamy dopad na bezpečnosť prevádzky na cestnej komunikácii

Metal-Rich SX Phe Stars in theKeplerField

High-resolution spectroscopic observations have been made for 32 of the 34 candidate SX Phe stars identified in the Kepler field by Balona & Nemec (2012). All available long- and short-cadence Q0-Q17 Kepler photometry has been analyzed for the 34 candidates. Radial velocities (RVs), space motions (U, V, W), projected rotation veloc- ities (v sin i), spectral types, and atmospheric characteristics (Teff , log g, [M/H], vmic, etc.) were derived from ∼160 spectra taken with the ESPaDOnS spectrograph on the Canada- France-Hawaii 3.6-m telescope and with the ARCES spectrograph on the Apache Point Observatory 3.5-m telescope. Two thirds of the stars are fast rotators with v sin i > 50 km/s, including four stars with v sin i > 200 km/s. Three of the stars have (negative) RVs > 250 km/s and retrograde space motions, and seven stars have total space motions > 400 km/s. All the spectroscopically measured SX Phe candidates have positions in a Toomre diagram that are consistent with being bona fide halo and thick-disk stars. Although several stars show a marked metal weakness, the mean [Fe/H] of the sample is near 0.0 dex (σ ∼ 0.25 dex), which is considerably more metal-rich than is normally expected for a sample of Pop. II stars. Observed pulsation frequency modulations and optical time delays suggest that at least eight of the SX Phe stars are in binary systems, some of which show signif- icant RV variations. Six of the time-delay binaries have secondary masses ranging from 0.05 to 0.70 Mo and orbital periods in the range 9 to 1570 days. Another star appears to be an ellipsoidal variable with a 2.3-day orbital period; and two other systems have orbital periods longer than the ∼4-year sampling interval of the Kepler data

Impacts of the Euro on the Slovenian Tourism Industry

This paper examines the impacts of the Euro adoption in Slovenia on its tourism. For this purpose, the empirical research among foreign tourists in Slovenia was conducted on their perceptions of the Euro adoption in Slovenia during the second half of 2007. The multivariate factor analysis was performed, which confirmed the four common dimensions of the Euro impacts on Slovenian tourism: attractiveness, costs, expensiveness, and comparison. The mean values of the analyzed items indicate the most positive impacts of the Euro on the direct price comparison and the easiness of comparison among tourist destinations in the Euro zone. The empirical results suggest that the Euro adoption has had the greatest impacts on better comparisons among tourist destinations in the Euro zone, followed by a significant decline in travel-operational costs. The increase in the expensiveness of the destination among foreign tourists is confirmed, whereas no significant improvement in the attractiveness of Slovenia as a tourist destination was proved after the Euro adoption.the Euro adoption, European Union, Slovenian tourism, multivariate factor analysis

Thermodynamic equilibrium conditions of graphene films on SiC

First-principles surface phase diagrams reveal that epitaxial monolayer graphene films on the Si side of 3C-SiC(111) can exist as thermodynamically stable phases in a narrow range of experimentally controllable conditions, defining a path to the highest-quality graphene films. Our calculations are based on a van der Waals corrected density functional. The full, experimentally observed (6 sqrt(3)x 6 sqrt(3))-R30 supercells for zero- to trilayer graphene are essential to describe the correct interface geometries and the relative stability of surface phases and possible defects

Minimizing Sonic Boom Through Simulation-Based Design: The X-59 Airplane

One of NASAs six Strategic Thrusts for aeronautics is Innovation in Commercial Supersonic Aircraft, with a vision of fast air travel widely available to the traveling public. Future supersonic aircraft will be efficient, affordable, and environmentally responsible, generating an acceptable level of en-route noise (sonic booms). The first major step is the ongoing construction of the new X-59 Quiet SuperSonic Technology X-plane to demonstrate technologies that reduce sonic booms to gentle thumps. By using highresolution Cart3D computational fluid dynamics simulations, the shape of the aircraft can be designed to control the non-linear interactions of shock waves to reduce the sonic boom noise on the ground to within outdoor ambient levels, thereby enabling supersonic overland flight