An exchange-correlation energy for a two-dimensional electron gas in a magnetic field

We present the results of a variational Monte Carlo calculation of the exchange-correlation energy for a spin-polarized two-dimensional electron gas in a perpendicular magnetic field. These energies are a necessary input to the recently developed current-density functional theory. Landau-level mixing is included in a variational manner, which gives the energy at finite density at finite field, in contrast to previous approaches. Results are presented for the exchange-correlation energy and excited-state gap at $\nu =$ 1/7, 1/5, 1/3, 1, and 2. We parameterize the results as a function of $r_s$ and $\nu$ in a form convenient for current-density functional calculations.Comment: 36 pages, including 6 postscript figure

Quantum interference from sums over closed paths for electrons on a three-dimensional lattice in a magnetic field: total energy, magnetic moment, and orbital susceptibility

We study quantum interference effects due to electron motion on a three-dimensional cubic lattice in a continuously-tunable magnetic field of arbitrary orientation and magnitude. These effects arise from the interference between magnetic phase factors associated with different electron closed paths. The sums of these phase factors, called lattice path-integrals, are ``many-loop" generalizations of the standard ``one-loop" Aharonov-Bohm-type argument. Our lattice path integral calculation enables us to obtain various important physical quantities through several different methods. The spirit of our approach follows Feynman's programme: to derive physical quantities in terms of ``sums over paths". From these lattice path-integrals we compute analytically, for several lengths of the electron path, the half-filled Fermi-sea ground-state energy of noninteracting spinless electrons in a cubic lattice. Our results are valid for any strength of the applied magnetic field in any direction. We also study in detail two experimentally important quantities: the magnetic moment and orbital susceptibility at half-filling, as well as the zero-field susceptibility as a function of the Fermi energy.Comment: 14 pages, RevTe

Exchange and correlation energies of ground states of atoms and molecules in strong magnetic fields

Using a Hartree-Fock mesh method and a configuration interaction approach based on a generalized Gaussian basis set we investigate the behaviour of the exchange and correlation energies of small atoms and molecules, namely th e helium and lithium atom as well as the hydrogen molecule, in the presence of a magnetic field covering the regime B=0-100a.u. In general the importance of the exchange energy to the binding properties of at oms or molecules increases strongly with increasing field strength. This is due to the spin-flip transitions and in particular due to the contributions of the tightly bound hydrogenic state s which are involved in the corresponding ground states of different symmetries. In contrast to the exchange energy the correlation energy becomes less relevant with increasing field strength. This holds for the individual configurations constituting the ground state and for the crossovers of the global ground state.Comment: 4 Figures acc.f.publ.in Phys.Rev.

Перспективы наращивания производства биогаза в Украине и Польше

У статті проаналізовано сучасний стан забезпеченості України та Польщі природним газом. В контексті зменшення залежності від вичерпних мінеральних ресурсів оцінено потенціал відновлюваних джерел енергії, зокрема виробництва біогазу в обох країнах. При цьому визначено, що важливу роль для подальшого його нарощування виробництва відіграє законодавче регулювання. Теоретичною і методичною основою даного дослідження є положення економічної теорії, наукові розробки вітчизняних і зарубіжних інженерів, економістів, експертів з питань розвитку біоенергетичної галузі, законодавчі та нормативні акти України та Польщі, а також статистичні дані обох країн.In the article is analyzed the current state of natural gas provision in Ukraine and Poland. In the context of reducing dependence on mineral resources are considered potential of renewable energy sources, including biogas production in both countries. There is determined that an important role for further increase production plays legislative regulation. Theoretical and methodological basis for this study found on economic theory, scientific development of domestic and foreign engineers, economists, experts in the field of bioenergy, legislative and normative acts of Ukraine and Poland, as well as statistics in both countries.В статье проанализировано современное состояние обеспеченности Украины и Польши природным газом. В контексте уменьшения зависимости от исчерпывающих минеральных ресурсов рассмотрен потенциал возобновляемых источников энергии, в частности, производства биогаза в обеих странах. При этом оценено, что важную роль для дальнейшего его наращивания производства играет законодательное регулирование. Теоретической и методической основой исследования являются положения экономической теории, научные разработки отечественных и зарубежных инженеров, экономистов, экспертов по вопросам развития биоэнергетической отрасли, законодательные и нормативные акты Украины и Польши, а также статистические данные обеих стран

Quantum Hall effect in single wide quantum wells

We study the quantum Hall states in the lowest Landau level for a single wide quantum well. Due to a separation of charges to opposite sides of the well, a single wide well can be modelled as an effective two level system. We provide numerical evidence of the existence of a phase transition from an incompressible to a compressible state as the electron density is increased for specific well width. Our numerical results show a critical electron density which depends on well width, beyond which a transition incompressible double layer quantum Hall state to a mono-layer compressible state occurs. We also calculate the related phase boundary corresponding to destruction of the collective mode energy gap. We show that the effective tunneling term and the interlayer separation are both renormalised by the strong magnetic field. We also exploite the local density functional techniques in the presence of strong magnetic field at $\nu=1$ to calculate renormalized $\Delta_{SAS}$. The numerical results shows good agreement between many-body calculations and local density functional techniques in the presence of a strong magnetic field at $\nu=1$. we also discuss implications of this work on the $\nu=1/2$ incompressible state observed in SWQW.Comment: 30 pages, 7 figures (figures are not included

Density-functional calculation of ionization energies of current-carrying atomic states

Current-density-functional theory is used to calculate ionization energies of current-carrying atomic states. A perturbative approximation to full current-density-functional theory is implemented for the first time, and found to be numerically feasible. Different parametrizations for the current-dependence of the density functional are critically compared. Orbital currents in open-shell atoms turn out to produce a small shift in the ionization energies. We find that modern density functionals have reached an accuracy at which small current-related terms appearing in open-shell configurations are not negligible anymore compared to the remaining difference to experiment.Comment: 7 pages, 2 tables, accepted by Phys. Rev.

Применение экспертно-математического метода для оценки риска потери урожая в результате неисправности сельскохозяйственной техники

Оценка риска потери урожая является достаточно сложным процессом, но имеет важное значение при выборе тракторов и сельскохозяйственных машин для хозяйства. Потери урожая зависят от меняющихся производственных условий, поэтому и риск возникновения таких потерь также может быть разным. В статье представлен экспертно-математический метод оценки риска, который все шире применяется при решении сложных экономических и управленческих задач

Anatomic dissociation of selective and suppressive processes in visual attention

Visual spatial attention is associated with activation in parietal regions as well as with modulation of visual activity in ventral occipital cortex. Within the parietal lobe, localisation of activity has been hampered by variation in individual anatomy. Using fMRI within regions of interest derived from individual functional maps, we examined the response of superior parietal lobule, intraparietal sulcus, and ventral occipital cortex in 11 normal adults as attention was directed to the left and right visual hemifields during bilateral visual stimulation. Activation in ventral occipital cortex was augmented contralateral to the attended hemifield (p < 0.006), while intraparietal activation was augmented ipsilaterally (p < 0.009), and superior parietal lobule showed no modulation of activity as a function of attended hemifield. These findings suggest that spatial enhancement of relevant stimuli in ventral occipital cortex is complemented by an intraparietal response associated with suppression of, or preparation of a reflexive shift of attention towards, irrelevant stimuli. The spatial attention system in superior parietal cortex, in contrast, may be driven to equal degrees by currently attended stimuli and by stimuli that are potential targets of attention

Можливості і перешкоди на шляху розвитку біопалива для транспорту в Польщі - досвід для України

The development of the biofuels sector largely depends on the political factors. The European Union decision, concerning the reduction of the share of the 1st generation biocomponents in transport fuels is a threat to the Polish industrial production of biofuels, which is 100 per cent based on the first-generation biofuels. Distilleries, producing bioethanol added to gasoline are particularly at risk. The difficult situation touches the oil pressing plants (esters added to diesel). The hazard primarily affects smaller plants of the biofuel sector. National giants, who intend to invest in the second and third generation biofuels that are not derived from food products are in a slightly better situation.Polish example, which has invested substantial financial resources in the development of the 1st generation biofuels, reaching its highest share in transport fuels in Europe, shows that in the case of Ukraine, the choice of strategy in the production of biofuels should be preceeded by a thorough analysis of the trends that are taking place in the European Union, including Poland. Therefore, there is a need to further study the situation in the EU biofuels, as well as for close scientific cooperation with Polish academics.Развитие возобновляемых источников энергии в производстве транспортного биотоплива имеет важное значение как для экономики Польши, так и Украины. Развитие сектора биотоплива зависит от ряда экономических и экологических факторов, в том числе политических решений. В статье представлено текущее состояние развития производства биотоплива в Польше, а также возможности и препятствия на пути развития этого сектора. Розвиток відновлювальних джерел енергії у виробництві транспортного біопалива має важливе значення як для економіки Польщі, так і України. Розвиток сектора біопалива залежить від ряду економічних та екологічних чинників, у тому числі політичних рішень. У статті представлено поточний стан розвитку біопалива в Польщі, а також можливості та перешкоди на шляху розвитку цього сектора

Cost analysis of cultural practices with the application of farm tractors with varying technical sophistication

Analizowano koszty wybranych zabiegów agrotechnicznych wykonywanych ciągnikami o zróżnicowanym stopniu zaawansowania technicznego. Potwierdzono wpływ zaawansowania technicznego ciągników na koszty wykonywanych zabiegów agrotechnicznych. Najwyższe koszty wykonania zabiegów agrotechnicznych generują ciągniki wysoko zaawansowane charakteryzujące się wyższą ceną. Stwierdzono, że tańsze modele z grupy ciągników wysoko zaawansowanych generują niższe koszty niż droższe modele z grupy ciągników średnio zaawansowanych.Stanisław Zają