On the use of scans at a constant ratio of B/E for studying decompositions of peptide metal(II)-ion complexes formed by electrospray ionization

The use of sector mass spectrometers to study metastable ion decompositions of peptide metal-ion complexes formed by electrospray ionization is discussed. Products that are formed by charge-separation reactions are characterized by large kinetic energy release distributions. This causes scans at a constant B/E to give incorrect product ion abundances and possibly incorrect mass assignments. Two instrumental methods exist that can be used either to detect the ions or to estimate relative ion abundances: a floated collision cell or mass-analyzed ion kinetic energy spectrometry (MIKES) scans. The floated collision cell, by virtue of an altered B/E scan law, however, discriminates against important metastable ion reactions that occur outside the cell. MIKES scans provide a clearer estimate of product ions that arise by metastable ion charge-separation reactions. Problems with pseudotandem (first field-free region) experiments are also discussed.     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Microstructural evolution of ZnS during sintering monitored by optical and positron annihilation techniques

Positron lifetime and optical absorption techniques were employed to track the microstructural evolution of polycrystalline ZnS grown by Chemical Vapor Deposition (CVD). As grown material and material treated with Hot Isostatic Pressure (HIP) was sintered at temperatures ranging from 400 to 1000°C for 2–18 h. A 290 ps defect lifetime could be resolved in all samples, while an additional longer lifetime (=430 ps) was found only in samples annealed at low temperatures. This component gradually disappeared during annealing at 800°C. Associated with the disappearance of the long-lived component, the apparent bulk lifetime of the material changed from 235 to 215 ps. A 215±2 ps bulk parameter was also found for HIP-treated material annealed at temperatures greater than 400°C and hence is taken to represent the delocalized state of the positrons in ZnS. Optical absorption measurements showed that annealing at 800°C also caused the absorption profiles of the CVD and HIP samples to converge. The rate of the bulk lifetime transition correlates with the absorption changes. The observed sharpening of the absorption profile is attributed to a decrease in scattering from grain boundaries and voids, and a decrease in absorption from point defects. The 430 ps lifetime is believed to be due to trapping at voids and grain boundaries, while the 290 ps lifetime likely is due to a monovacancy stabilized as a small complex.Paper presented at the 132nd WE-Heraeus-Seminr on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Multiphoton absorption and luminescence of osmium tetroxide

Both the multiphoton absorption and the luminescence brightness of osmium tetroxide induced by absorption of temporally smooth CO₂ 10P(20) laser pulses of 10 and 40 ns FWHM have been measured for pressures in the range 6.7 to 200 Pa. A dependence of these phenomena on laser pulse length is observed. Comparison of the luminescence brightness to the average excitation shows that the distribution of the multiphoton excitation depends on the laser pulse intensity for the two pulse lengths studied.Issued as AECL Contribution No. 8806     

i-perfectm-cycle systems,m ≤ 19

Summary For allm 19 and each meaningful value ofi (2 i m/2), the spectrum problem fori-perfectm-cycle systems is examined.     

Search for heavy particles decaying into electron-positron pairs in pp collisions

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.     

Enhanced locking region in injection-locked two-section lasers

In this Letter, we investigate the criteria for achieving an enhanced stable locking region in the parameter space of injected field E_inj and frequency detuning ω in two-section semiconductor lasers subject to optical injection. Using the rate equations, a stability analysis is performed and the conditions for an enhanced locking region are deduced from the requirement for the average linewidth enhancement factor appearing in the locking-bandwidth equation to be close to zero. We calculate a stability map for an injection-locked two-section laser with an almost-symmetrical locking region that is greatly enhanced compared to a single-section injection-locked laser with identical material and control parameters.     

The minimum span of L(2,1)-labelings of certain generalized Petersen graphs

In the classical channel assignment problem, transmitters that are sufficiently close together are assigned transmission frequencies that differ by prescribed amounts, with the goal of minimizing the span of frequencies required. This problem can be modeled through the use of an L(2,1)-labeling, which is a function f from the vertex set of a graph G to the non-negative integers such that |f(x)-f(y)|? 2 if xand y are adjacent vertices and |f(x)-f(y)|?1 if xand y are at distance two. The goal is to determine the λ-number of G, which is defined as the minimum span over all L(2,1)-labelings of G, or equivalently, the smallest number k such that G has an L(2,1)-labeling using integers from {0,1,…,k}. Recent work has focused on determining the λ-number of generalized Petersen graphs (GPGs) of order n. This paper provides exact values for the λ-numbers of GPGs of orders 5, 7, and 8, closing all remaining open cases for orders at most 8. It is also shown that there are no GPGs of order 4, 5, 8, or 11 with λ-number exactly equal to the known lower bound of 5, however, a construction is provided to obtain examples of GPGs with λ-number 5 for all other orders. This paper also provides an upper bound for the number of distinct isomorphism classes for GPGs of any given order. Finally, the exact values for the λ-number of n-stars, a subclass of the GPGs inspired by the classical Petersen graph, are also determined. These generalized stars have a useful representation on Möebius strips, which is fundamental in verifying our results.     

Study of the semileptonic charm decays D(0)-->pi(-)l(+)nu and D(0)-->K(-)l(+)nu

We investigate the decays D(0)-->pi(-)l(+)nu and D(0)-->K(-)l(+)nu, where l is e or mu, using approximately 7 fb(-1) of data collected with the CLEO III detector. We find R(0) identical with B(D(0)-->pi(-)e(+)nu)/B(D(0)-->K(-)e(+)nu)=0.082+/-0.006+/-0.005. Fits to the kinematic distributions of the data provide parameters describing the form factor of each mode. Combining the form factor results and R(0) gives |f(pi)(+)(0)|(2)|V(cd)|(2)/|f(K)(+)(0)|(2)|V(cs)|(2)=0.038(+0.006+0.005)(-0.007-0.003).