On the Timing of the Peak Mean and Variance for the Number of Customers in an M(t)/M(t)/1 Queueing System

Revised October 1994This paper examines the time lag between the peak in the arrival rate and the peaks in the mean and variance for the number of customers in an M(t)/M(t)/1l system. We establish a necessary condition for the time at which the peak in the mean is achieved. In cases in which system utilization exceeds one during some period, we show that the peak in the mean occurs after the end of this period

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV

We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)3NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 × 10−16 cm2, while fragmentation through DI results mainly in the formation of the bare metal cation Co+ with a maximum cross section close to 4.6 × 10−16 cm2 at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes

Synthetic Analogues of the Snail Toxin 6-Bromo-2-mercaptotryptamine Dimer (BrMT) Reveal That Lipid Bilayer Perturbation Does Not Underlie Its Modulation of Voltage-Gated Potassium Channels

Drugs do not act solely by canonical ligand–receptor binding interactions. Amphiphilic drugs partition into membranes, thereby perturbing bulk lipid bilayer properties and possibly altering the function of membrane proteins. Distinguishing membrane perturbation from more direct protein–ligand interactions is an ongoing challenge in chemical biology. Herein, we present one strategy for doing so, using dimeric 6-bromo-2-mercaptotryptamine (BrMT) and synthetic analogues. BrMT is a chemically unstable marine snail toxin that has unique effects on voltage-gated K+ channel proteins, making it an attractive medicinal chemistry lead. BrMT is amphiphilic and perturbs lipid bilayers, raising the question of whether its action against K+ channels is merely a manifestation of membrane perturbation. To determine whether medicinal chemistry approaches to improve BrMT might be viable, we synthesized BrMT and 11 analogues and determined their activities in parallel assays measuring K+ channel activity and lipid bilayer properties. Structure–activity relationships were determined for modulation of the Kv1.4 channel, bilayer partitioning, and bilayer perturbation. Neither membrane partitioning nor bilayer perturbation correlates with K+ channel modulation. We conclude that BrMT’s membrane interactions are not critical for its inhibition of Kv1.4 activation. Further, we found that alkyl or ether linkages can replace the chemically labile disulfide bond in the BrMT pharmacophore, and we identified additional regions of the scaffold that are amenable to chemical modification. Our work demonstrates a strategy for determining if drugs act by specific interactions or bilayer-dependent mechanisms, and chemically stable modulators of Kv1 channels are reported

Cross sections for electron impact excitation of the C 1 and D 1+ electronic states in N2O

Differential and integral cross sections for electron-impact excitation of the dipole-allowed C 1Π and D 1Σ+ electronic states of nitrous oxide have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at six electron energies in the range 15–200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to check both the validity of the only other comprehensive experimental study into these excitation processes and to extend the energy range of those data. Agreement with the earlier data, particularly at the lower common energies, was typically found to be fair. In addition, the BEf-scaling approach is used to calculate integral cross sections for the C 1Π and D 1Σ+ states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, the only exception being at the lowest energies of this study. Finally, optical oscillator strengths, also determined as a part of the present investigations, were found to be in fair accordance with previous corresponding determinations

A queueing theoretic approach to set staffing levels in time-dependent dual-class service systems

This article addresses the optimal staffing problem for a nonpreemptive priority queue with two customer classes and a time-dependent arrival rate. The problem is related to several important service settings such as call centers and emergency departments where the customers are grouped into two classes of “high priority” and “low priority,” and the services are typically evaluated according to the proportion of customers who are responded to within targeted response times. To date, only approximation methods have been explored to generate staffing requirements for time-dependent dual-class services, but we propose a tractable numerical approach to evaluate system behavior and generate safe minimum staffing levels using mixed discrete-continuous time Markov chains (MDCTMCs). Our approach is delicate in that it accounts for the behavior of the system under a number of different rules that may be imposed on staff if they are busy when due to leave and involves explicitly calculating delay distributions for two customer classes. Ultimately, we embed our methodology in a proposed extension of the Euler method, coined Euler Pri, that can cope with two customer classes, and use it to recommend staffing levels for the Welsh Ambulance Service Trust (WAST)

Stabilisation Clauses in Investment Agreements - a Human Rights and Development Perspective

When making a long-term investment investors need to be able to ensure a certain degree of legal and financial predictability. Since the investment is subject to the jurisdiction of the host state, investment agreements between the host state and the investor are commonly used. Such investment agreements may include stabilisation clauses, ensuring that arbitrary changes in law do not apply to the investment or that compensation will be rewarded where the changes lead to increased costs for the investor. However, in recent years, a debate on the negative human rights impacts of stabilisation clauses has surfaced. In cases where a stabilisation clause is written to hinder changes in law also concerning human rights, it may have detrimental effects on the development of human rights in the host state. When the host state is a developing country, the issue becomes especially prominent. In March 2011 the United Nations published the Guiding Principles on Business and Human Rights, establishing a corporate responsibility to respect human rights and human rights due diligence to be an incorporated part of businesses. Although voluntary in character, the UN Guiding Principles changes the way business and human rights are looked at. This paper is intended to analyse the impacts of the UN Guiding Principles on the future use of stabilisation clauses and provides a description of stabilisation clauses in relation to human rights in developing countries. By looking into aspects of foreign direct investment, human rights, the business and human rights debate and the recent changes on corporate responsibilities this paper is meant to raise questions concerning the use of stabilisation clauses as a means to secure foreign investments. The different forces and interests behind the use of stabilisation clauses are considered, and focus lies upon why the use of stabilisation clauses is especially problematic where the host state is a developing country. The often-confidential character of stabilisation clauses, or rather the investment agreements in which they are included, poses a true challenge. The number of cases available for research is comparatively low, and cases of corporate-related human rights abuses are most often referred to arbitration. Nevertheless, it becomes evident that stabilisation clauses, if drafted to include changes in human rights law, may have detrimental effects on human rights. In this sense, the inclusion of stabilisation clauses in investment contracts directly contradicts the entire concept of a corporate responsibility to respect human rights and the purpose of human rights due diligence as set forth by the UN Guiding Principles

Substitution effects in elastic electron collisions with CH3X (X = F, Cl, Br, I) molecules

We report absolute elastic differential, integral, and momentum transfer cross sections for electron interactions with the series of molecules CH3X (X = F, Cl, Br, I). The incident electron energy range is 50–200 eV, while the scattered electron angular range for the differential measurements is 15°–150°. In all cases the absolute scale of the differential cross sections was set using the relative flow method with helium as the reference species. Substitution effects on these cross sections, as we progress along the halomethane series CH3F, CH3Cl, CH3Br, and CH3I, are investigated as a part of this study. In addition, atomic-like behavior in these scattering systems is also considered by comparing these halomethane elastic cross sections to results from other workers for the corresponding noble gases Ne, Ar, Kr, and Xe, respectively. Finally we report results for calculations of elastic differential and integral cross sections for electrons scattering from each of the CH3X species, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements was found to be quite remarkable in each case

A study of electron scattering from benzene: excitation of the 1B1u, 3E2g, and 1E1u electronic states

We report results from measurements for differential and integral cross sections of the unresolved 1B1u and 3E2g electronic states and the 1E1u electronic state in benzene. The energy range of this work was 10–200 eV, while the angular range of the differential cross sections was -3°–130°. To the best of our knowledge there are no other corresponding theoretical or experimental data against which we can compare the present results. A generalized oscillator strength analysis was applied to our 100 and 200 eV differential cross section data, for both the 1B1u and 1E1u states, with optical oscillator strengths being derived in each case. The respective optical oscillator strengths were found to be consistent with many, but not all, of the earlier theoretical and experimental determinations. Finally, we present theoretical integral cross sections for both the 1B1u and 1E1u electronic states, as calculated within the BEf-scaling formalism, and compare them against relevant results from our measurements. From that comparison, an integral cross section for the optically forbidden 3E2g state is also derived

A-band methyl halide dissociation via electronic curve crossing as studied by electron energy loss spectroscopy

Excitation of the A-band low-lying electronic states in the methyl halides, CH3I, CH3Br, CH3Cl, and CH3F, has been investigated for the (n→σ∗) transitions, using electron energy loss spectroscopy (EELS) in the range of 3.5–7.5 eV. For the methyl halides, CH3I, CH3Br, and CH3Cl, three components of the Q complex (3Q1, 3Q0, and 1Q1) were directly observed, with the exception of methyl fluoride, in the optically forbidden EELS experimental conditions of this investigation. The effect of electronic-state curve crossing emerged in the transition probabilities for the 3Q0 and 1Q1 states, with spin-orbit splitting observed and quantified against results from recent ab initio studies