A Note on π-Engel Conditions

In this paper we show that the weakly v35vj40621730643/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">v35vj40621730643/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">-Engel conditions are closely related to the existance of normal v35vj40621730643/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-complements; while the v35vj40621730643/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">v35vj40621730643/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">-Engel conditions are closely related to the v35vj40621730643/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-nilpotent groups.AMS Subject Classification (2000): 20D20     

Crystal structures of 4,7-phenanthrolino-5,6:5′,6′-pyrazine tetrahydrate and 1,4,5,8,9,12-hexaazatriphenylene dihydrate

The crystal structures of 4,7-phenanthrolino-5,6:5v586/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">,6v586/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-pyrazine tetrahydrate (I) and 1,4,5,8,9,12-hexaazatriphenylene dihydrate (II) have been determined from low temperature (173 K) x-ray single crystal diffraction data. I crystallizes in the triclinic system, space group P v586/10870_2004_Article_224780_TeX2GIFIE1.gif" alt=" $$\overline 1$$ " align="middle" border="0"> with a = 11.2687(6), b = 12.4766(6), c = 12.7068(7) Å, v586/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"> = 113.4740(10), v586/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = 91.605(2), v586/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0"> = 114.587(2)°, V = 1449.33(13) ų, and Z = 4. II crystallizes in the orthorhombic system, space group Pca2₁ with a = 18.187(2), b = 9.2576(11), c = 6.9672(8) Å, V = 1173.0(2) ų, and Z = 4. In both structures the planar heterocyclic molecules stack with interplanar distances down to 3.3 Å, which is consistent with self-v586/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-complexation. The crystal water molecules provide links between the columns of stacked molecules through hydrogen bonds. In each compound the N-C bond lengths fall into two distinct groups (mean values 1.330(3) vs 1.361(1) Å in I and 1.320(3) vs 1.357(5) Å in II), as do the C-C bonds of the central phenyl rings (1.411(4) vs 1.467(1) Å in I and 1.405(5) vs 1.458(4) Å in II).     

Production systems with interruptions, arbitrary topology and finite buffers

We consider a production system with finite buffers and arbitrary topology where service time is subject to interruptions in one of three ways, viz. machine breakdown, machine vacations or Nv727102r173h543h/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">policy. We develop a unified approximation (analytical) methodology to calculate the throughput of the system using queueing networks together with decomposition, isolation and expansion techniques. The methodology is rigorously tested covering a large experimental region. Orthogonal arrays are used to design the experiments in order to keep the number of experiments manageable. The results obtained using the approximation methodology are compared to the simulation results. The tv727102r173h543h/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">tests carried out to investigate the differences between the two results show that they are statistically insignificant. Finally, we test the methodology by applying it to several arbitrary topology networks. The results show that the performance of the approximation methodology is consistent, robust and produces excellent results in a variety of experimental conditions.     

The surjectivity of the canonical homomorphism from singular homology to Cech homology

Let be a locally -connected compact metric space. Then, the canonical homomorphism from the singular homology group to the Cech homology group is surjective. Consequently, if a compact metric space is locally connected, then the canonical homomorphism from to is surjective.

     

Convergence de mesures spectrales aléatoires et applications à des principes d'invariance

Nous présentons un cadre unificateur pour un certain nombre de résultats connus de convergence en loi pour des processus admettant une représentation linéaire par rapport à un bruit blanc faible pour lequel il existe un principe dv/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">invariance faible. Nous montrons que ce principe dv/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">invariance est équivalent à la convergence dv/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">une suite de mesures aléatoires spectrales. Ceci permet dv/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">affaiblir les hypothèses usuelles et donc dv/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">obtenir des résultats nouveaux de convergence en loi, notamment pour des processus à longue portée.     

A GaAs–InGaAs optoelectronic switch with multiple operation states

An optoelectronic switch with both n- and p-type delta-doped (v6640182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped) quantum wells was investigated. The v6640182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped structures formed potential wells for the carrier accumulation and potential barriers for the carrier injection. Being possessed of v6640182n16137/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-doped sheets with different doping levels, the potential barriers were sequentially collapsed to produce a double negative-differential-resistance (NDR) phenomenon in the current–voltage (I–V) characteristics of the device, due to the carrier accumulation in the potential wells. The device also showed an optical function related to the barrier heights controllable by incident light.     

Monte Carlo simulations of electron dynamics in N2/CO2 mixtures

Motivated by experimental investigations of electrical discharges in N₂/CO₂/H₂O, Monte Carlo (MC) electron dynamics simulations in atmospheric N₂/CO₂ mixtures were performed. The goal was to obtain electron energy distribution functions (EEDFs), mean free path, drift velocity, collision frequency and mean energy of electrons, rate coefficients of electron-impact reactions, ionisation and attachment coefficients, as functions of the reduced electric field strength (E/N) and of the concentration of individual gas components. The results obtained by MC simulations were fitted with polynomials of up to the 3rd order with reasonable accuracy for E/N above 80 Td. The studied parameters below 80 Td were strongly non-linear as functions of E/N. This is mostly due to the influence of elastic collisions of electrons with CO₂ molecules prevailing in CO₂-dominant mixtures for E/N < 40 Td, and vibrational excitation collisions of N₂ species prevailing in N₂-dominant mixtures for E/N from 40 to 80 Td. The effect of these electron-impact processes was specific for each of the studied parameters.     

Structure of low-lying <Superscript>12</Superscript>C resonances

The hyperspherical adiabatic expansion is combined with complex scaling and used to calculate low-lying nuclear resonances of ¹²C in the 3α model. We use Ali-Bodmer potentials and compare results for other potentials α-α with similar ⁸Be properties. A three-body potential is used to adjust the ¹²C resonance positions to desired values extending the applicability of the method to many-body systems decaying into three α-particles. For natural choices of three-body potentials we find 14 resonances below the proton separation threshold, i.e. two 0⁺, three 2⁺, two 4⁺, one of each of 1^±, 2^-, 3^±, 4^-, and 6⁺. The partial-wave decomposition of each resonance is calculated as a function of the hyperradius. Strong variation is found from small to large distance. The connection to previous experimental and theoretical results is discussed and agreements as well as disagreements are emphasized.     

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

High-precision vector and tensor analyzing powers of elastic deuteron-proton ( d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70^°-120^° in the center-of mass frame for incident-deuteron energies E _d ^lab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(2⁺) reaction at 0^°. Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high-precision data consistently and requires, therefore, further investigation.