Critical Point of an Interacting Two-Dimensional Atomic Bose Gas

We have measured the critical atom number in an array of harmonically trapped two-dimensional (2D) Bose gases of rubidium atoms at different temperatures. We found this number to be about five times higher than predicted by the semi-classical theory of Bose-Einstein condensation (BEC) in the ideal gas. This demonstrates that the conventional BEC picture is inapplicable in an interacting 2D atomic gas, in sharp contrast to the three-dimensional case. A simple heuristic model based on the Berezinskii-Kosterlitz-Thouless theory of 2D superfluidity and the local density approximation accounts well for our experimental results

Second harmonic generation in nonlinear transformation of electromagnetic waves in suddenly created cold magnetized plasma: Transversal propagation

U radu je analizirana transformacija izvornog linearno polarizovanog elektromagnetskog talasa, usled slabih nelinearnosti, u elektronske i elektromagnetske oscilacije, stacionarne (prostorno promenljive i jednosmerne) i talasne elektromagnetske i elektronske modove u plazmi primenom perturbacione teorije drugog reda. Efikasnost eksitacije transverzalnih električnih modova, dvostruko veće frekvencije i dvostruko većeg talasnog broja od modova dobijenih u linearnoj teoriji, analizirana je za različite vrednosti ugaone frekvencije izvornog talasa i za vrednost ugaone elektronske žiro-frekvencije koja odgovara vrednosti ugaone elektronske razmene frekvencije.The nonlinear transformation of linearly polarized source electromagnetic wave in electron and electromagnetic plasma oscillations, stationary (rectification and space-varying) modes and travelling electron and electromagnetic plasma waves, due to a weak nonlinearity, has been analyzed by using the second order perturbation theory in radio approximation. The efficiency of excitation of the transversal secondharmonic electric wave modes with double wave number with respect to the wave number modes in the linear transformation has been studied for different values of source wave frequency, taking the electron cyclotron frequency as a parameter)

Second harmonic generation in nonlinear transformation of electromagnetic waves in suddenly created cold magnetized plasma: Transversal propagation

U radu je analizirana transformacija izvornog linearno polarizovanog elektromagnetskog talasa, usled slabih nelinearnosti, u elektronske i elektromagnetske oscilacije, stacionarne (prostorno promenljive i jednosmerne) i talasne elektromagnetske i elektronske modove u plazmi primenom perturbacione teorije drugog reda. Efikasnost eksitacije transverzalnih električnih modova, dvostruko veće frekvencije i dvostruko većeg talasnog broja od modova dobijenih u linearnoj teoriji, analizirana je za različite vrednosti ugaone frekvencije izvornog talasa i za vrednost ugaone elektronske žiro-frekvencije koja odgovara vrednosti ugaone elektronske razmene frekvencije.The nonlinear transformation of linearly polarized source electromagnetic wave in electron and electromagnetic plasma oscillations, stationary (rectification and space-varying) modes and travelling electron and electromagnetic plasma waves, due to a weak nonlinearity, has been analyzed by using the second order perturbation theory in radio approximation. The efficiency of excitation of the transversal secondharmonic electric wave modes with double wave number with respect to the wave number modes in the linear transformation has been studied for different values of source wave frequency, taking the electron cyclotron frequency as a parameter)

Superconducting film with randomly magnetized dots: A realization of the 2D XY model with random phase shifts

We consider a thin superconducting film with randomly magnetized dots on top of it. The dots produce a disordered pinning potential for vortices in the film. We show that for dots with permanent and random magnetization normal or parallel to the film surface, our system is an experimental realization of the two-dimensional XY model with random phase shifts. The low-temperature superconducting phase, that exists without magnetic dots, survives in the presence of magnetic dots for sufficiently small disorder.Comment: 5 pages, 1 figur

Imidazole aldoximes effective in assisting butyrylcholinesterase catalysis of organophosphate detoxification.

Intoxication by organophosphate (OP) nerve agents and pesticides should be addressed by efficient, quickly deployable countermeasures such as antidotes reactivating acetylcholinesterase or scavenging the parent OP. We present here synthesis and initial in vitro characterization of 14 imidazole aldoximes and their structural refinement into three efficient reactivators of human butyrylcholinesterase (hBChE) inhibited covalently by nerve agent OPs, sarin, cyclosarin, VX, and the OP pesticide metabolite, paraoxon. Rapid reactivation of OP-hBChE conjugates by uncharged and nonprotonated tertiary imidazole aldoximes allows the design of a new OP countermeasure by conversion of hBChE from a stoichiometric to catalytic OP bioscavenger with the prospect of oral bioavailability and central nervous system penetration. The enhanced in vitro reactivation efficacy determined for tertiary imidazole aldoximes compared to that of their quaternary N-methyl imidazolium analogues is attributed to ion pairing of the cationic imidazolium with Asp 70, altering a reactive alignment of the aldoxime with the phosphorus in the OP-hBChE conjugate

Thermomechanical properties of PbSbSn alloys

Procesi elektrootpornog zavarivanja i lemljenja delova izrađenih od legura PbSbSn u industriji akumulatora tipa olovo-kiselina, u energetici, elektronici i hemijskoj industriji zahtevaju detaljna istraživanja termomehaničkih osobina ovih legura, koje zavise od temperature. Eksperimentalni rezultati koeficijenta provođenja toplote, dobijeni su upotrebom metode laserskog impulsa, zasnovanoj na matematičkoj analizi nestacionarnog jednodimenzijskog provođenja toplote kroz beskonačan ravan adijabatski zid. Rezultati toplotne provodljivosti dobijeni su iz merenja brzine porasta temperature na jednoj strani epruvete. Temperatura topljenja, latentna toplota i specifični toplotni kapacitet određeni su korišćenjem kalorimetra. Koeficijent linearnog širenja je određen korišćenjem visoko temperaturnog dilatometra. Data je temperaturska zavisnost ispitivanih mehaničkih osobina. Eksperimentalni rezultati su predstavljeni za date PbSbSn legure, u kojima je sadržaj Sb ograničen do 3,5 %, a sadržaj Sn do 0,5 %. Svi dobijeni rezultati temperaturske zavisnosti termomehaničkih osobina su predstavljeni grafički i tabelarno.Resistance welding and soldering processes of parts made of PbSbSn alloys in the industry of lead-acid batteries, power engineering, electronics and chemical industry require a detailed research of thermomechanical properties of these alloys that depend on temperature. Data on thermal conductivity are acquired from experiments with a laser pulse method, and based on mathematical analysis of non-stationary one-dimensional heat conduction through an infinite flat adiabatic wall. Data on thermal conductance are determined from measurements of the temperature increase rate on one side of a sample. The melting temperature, latent heat and specific heat capacity are determined by calorimeter. The coefficient of linear expansion is determined by using a high-temperature dilatometer. Temperature dependence of tensile testing mechanical properties is also given. The experimental results are presented for the chosen PbSbSn alloys in which the Sb content is limited to 3.5 % and the content of Sn to 0.5 %. All results of temperature dependence of thermomechanical properties are given in graphical and tabular form

Towards automated design of quantum cascade lasers

We present an advanced technique for the design and optimization of GaAs/AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier–phonon and carrier–carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of lambda~9 µm GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures. © 2005 American Institute of Physic

Prostorna analiza tala i utjecaj na produktivnost u gospodarskoj jedinici Mužljanski rit

The paper presents analysis of soil spatial distribution and productivity of Populus x euramericana I-214 forest cultures in forest management unit (hereinafter: FMU) Muzljanski rit. Soil cover in the FMU is heterogeneous in relation to position and altitude in floodplain. Analysis were conducted on eugley and humogley soil types. Eugley, soil type, was delineated according to physiologically active soil depth as α, β or β/γ gley soils and humogley was delineated as one soil unit. Cultures of the poplar clones Populus x euramericana I-214 are found on at least two but usually more different site types within the same forest management section (18.43 %). Single forest management section is a by definition a single forest spatial unit having similar ecologic factors. Aim of our research was to enable consistent forest section delineation, based on the interaction of soil productivity properties and distribution as well as Populus x euramericana I-214 productivity dataset. Based on our anaysis (spatial analysis of raster layers of soil systematic unit distribution-soil subunit, digital elevation model and productivity according to inner delineation of FMU Muzljanski rit), the resuts show eugley share in lower systematic soil unit. The results show contribution of lower systematic units of eugley in forest managemet section/culture. We found a raising trend of α and β-gley, as well as humogley. On one side the higher contribution of this sistematic units indicates reduction in the forest culture yield. On the other side higher contribution of β/γ gley indicates an increase of culture yeald. The Populus x euramericana I-214 cultures are spatialy concentrated, extending over soil units with different characteristics, pointing in alternative economicaly justified section delineation, based on the soil types.Razumijevanje produktivnosti drveća u gospodarskim jedinicama vezano je za poznavanje više stanišnih čimbenika. U radu se prikazuju istraživanja s obzirom na rasprostranjenost tala, dajući im veću važnost u odnosu na izbor klona, vodni režim, klimatske ekstreme, kao i postupak obnove nasada. Opravdanost navedenog pristupa je vezana za više provedenih istraživanja, u kojima je jedan od osnovnih čimbenika tip tla, a s njime i odgovarajuća vrsta drveća.Pregled prostorne rasprostranjenosti tala omogućeno je razvojem programskih paketa za prostornu analizu geoinformacijskih podataka. U radu je prikazana analiza prostorne raspodjele tala i produktivnosti nasada Populus x euramericana I-214 gospodarske jedinice (GJ) Mužljanski Rit. Definiranju rasprostranjenosti tala u GJ Mužlјanski rit prethodila je izrada modela terena. Model terena napravljen je na bazi osnovne državne karte (R 1:5000) za definiranje mikrorelјefa. Svaka poznata točka je osim vrijednosti na x i y osi, dobila vrijednost i na z osi. U programskom paketu ArcGIS je izvršena interpolacija, a rezultat je 3D model terena u GJ Mužljanski rit na površini od približno 1820 ha. Na ovaj način je omogućena analizirati ekvidistance na 10 cm na prostoru gospodarske jedinice. Prostornom analizom su prema Klasifikaciji zemlјišta Jugoslavije (Škorić i sur., 1985) determinirani različiti tipovi i niže sistematske jedinice tala. Prethodno navedena klasifikacija je nadopunjena podjelom na fiziološki aktivnu dubinu profila prema Wildeu (1940), zbog pretpostavljene različite produktivnosti tala ovisno o vrsti stabala koja će se tamo uzgajati. Postupak je na ovaj način definirao područja niza i greda na prostoru čitave GJ, te je poslužio kao osnova za daljnje analize. Mrežom pedoloških profila su definirani tipovi tala. Rezultati istraživanja ukazuju da je pokrov tla u istraživanoj GJ heterogen, te su kao tipovi tla determinirani euglej i humoglej. Podjela na niže sistematske jedinice kod eugleja je vezana za fiziološki aktivnu dubinu profila i to na α, β ili β/γ glej (ograničavajući čimbenik je stagnacija podzemne vode u profilu). Posljedica je 18,43% nasada Populus x euramericana I-214 koji se nalazi na dvije ili više različitih vrsta sustavnih jedinica tala, unutar istog odsjeka, u dijelu šume koja tvori glavnu prostornu jedinicu sa sličnom ekologijom. Povećanje ili smanjenje udjela sustavne jedinice tla dovodi do postizanja različite produktivnosti. U radu je utvrđena potreba podjele eugleja kao tipa tla na niže sistematske jedinice. Rezultati istraživanja ukazuju da trendovi povećanja udjela α i β-gleja u tlu, kao i humogleja, utječu na smanjenje prinosa nasada Populus x euramericana I-214, dok udio β/γ-gleja (u statističkoj značajnosti od 0,3745) pozitivno korelira s volumenom nasada Populus x euramericana I-214. Iz rezultata je također vidljivo da je mali udio α gleja (do 10%) dovoljan po površini odsjeka da bi doveo do smanjenja produktivnosti nasada Populus x euramericana I-214, dok je taj udio kod β-gleja nešto veći te ne bi trebao prelaziti 20%, odnosno najviše 30%. Nasadi Populus x euramericana I-214 prostorno su koncentrirani, što ukazuje na alternativnu ekonomski održivu podjelu na temelju karakteristika tala uz izbor odgovarajuće vrste drveća. Na području niza je u najvećoj mjeri zastupljen euglej (fiziološki α i β glej) i potrebno ih je izbjegavati, budući da i mali udio navedenih sustavnih jedinica zemljišta bitno utječe na produktivnost, a posljedično i na sortimentne strukture nasada Populus x euramericana I-214. U najvećem broju slučajeva, kao zamjenska vrsta na humoglejevima i fiziološki plićim sustavnim jedinicama bio bi hrast lužnjak kao stabilna i vitalna vrsta. Na osnovi prostornog rasprostranjenja tala to se vrlo jasno može definirati, a u konačnici se i ispunjavaju ostale funkcije šuma

Electronics ceramics grain boundaries and complex fractal dimension

Analysis of ceramic grain boundaries, esspecially for BaTiO3 , is also important for its dielectric and conductive properties. In this regard, the fractal analysis was highlighted. The grain contacts geometry based on intergranular contact surface fractal morphology was the subject of our long term research. A new approach based on complex dimension fractal geometry and correlation between microstructurenanostructure and rare-earth properties and other additives doped BaTiO3-ceramics and electronics properties, is applied . In addition to the continuous type of scaling typical for real standard fractal objects, complex objects are considered here, which also have a discrete scaling symmetry with logarithmic space period. That rely on their appearance on the various , micro and macro, electrical and other properties of BaTiO3-ceramics

Imobilizacija Na,K-ATPpaze izolovane iz sinaptičkih plazma-membrana mozga pacova

Rat brain Na,K-ATPase partially purified by SDS from synaptic plasma membranes (SPM) was immobilized by adsorption on nitrocellulose (NC), polyvinylidene fluoride (PVDF) and glass fiber (GF) membranes, Partial SDS solubilization increased the enzyme activity by 40%. With regard to the presentation of the enzyme activity. nitrocellulose Was shown to be the optimal support for die immobilization, The enzyme showed the highest percentage activity (14%) after 30 min of SPM adsorption. at 20 degreesC under the vaccum. with 25 mug of proteins per NC disc filter. In addition, adsorption on NC stabilizes the Na,K-ATPase, since the activity was substantial 72 h after adsorption at 20 degreesC, After adsorption. the sensitivity of the enzyme to HgCl2 and CdCl2 inhibition was higher, The results show that immobilized Na,K-NTPase SPM can be used as a practical model for the detection of metal ions in different samples.Delimično prečišćena Na,K-ATPaza sinaptičkih plazma–membrana (SPM) mozga pacova imobilizovana je adsorpcijom na nitrocelulozne (NC) poliviniliden-fluorid (PVDF) membrane i membrane od staklenih vlakana (SV). Aktivnost enzima delimično prečišćenog solubilizacijom SDS-om povećana je oko 40%. Najveći procenat aktivnosti (14%) enzim zadržava posle 30 minuta adsorpcije SPM na 20ºC, pod vakuumom, sa 25 μg proteina po nitroceluloznom disku. Na,K-ATPaza imobilizovana na nitroceluloznoj membrani stabilna je 72 sata na 20ºC. Adsorpcijom, osetljivost enzima na inhibiciju Hg2+ i Cd2+ se povećava. Rezultati pokazuju da se imobilizovana Na,K-ATPaza SPM može koristiti za detekciju toksičnih metalnih jona u različitim uzorcima