bluuebunny/crossref_metadata_2025 huggingface dataset:
A bidirectional heuristic for maximizing the net present value of large‐scale projects subject to limited resources
Authors: Selle Thomas , Zimmermann Jürgen
Published: February 2003

We consider the scheduling of large‐scale projects to maximize the project net present value given temporal and resource constraints. The net present value objective emphasizes the financial aspects of project management. Temporal constraints between the start times of activities make it possible to handle practical problem assumptions. Scarce resources are an expression of rising cost. Since optimization techniques are not expedient to solve such problems and most heuristic methods known from literature cannot deal with general temporal constraints, we propose a new bidirectional priority‐rule based method. Scheduling activities with positive cash flows as early and activities with negative cash flows as late as possible results in a method which is completed by unscheduling techniques to cope with scarce resources. In a computational experiment, we compare the well‐known serial generation scheme where all activities are scheduled as early as possible with the proposed bidirectional approach. On the basis of a comprehensive data set known from literature containing instances with up to 1002 activities, the efficiency of the new approach is demonstrated. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2003
TQM self‐assessment evolves and promotes strategic learning at Ericsson España S.A.
Authors: Benavent Francisco Balbastre
Published: February 2003

Self‐assessment is a comprehensive, systematic, and regular review of an organization's
activities and results in reference to a business excellence model. This process allows the organization to
clearly discern its strengths and deficiencies, launch improvement plans, and monitor their progress. When
organizations repeatedly carry out this cycle of evaluation and action taking, they can achieve genuine and
sustained improvement.

Many firms have found self‐assessment to be an important tool for fostering continuous improvement,
one of the fundamental principles of total quality management (TQM). Indeed, self‐assessment
has been employed by the winners of the most important quality awards—the Deming Prize in Japan, the
Malcolm Baldrige National Quality Award in the United States, and the European Quality Award (EQA) in
Europe. Ericsson España S.A. (EESA), 1994 EQA winner, is among them. And the evolution of their
learnings from this effort has led them to a highly strategic focus. © 2003 Wiley Periodicals,
Inc.
Creative ways to empower action to change the organization: Cases in point
Authors: Kotter John P. , Cohen Dan S.
Published: February 2003

In the Winter 2002 issue, the affiliation of Dan S. Cohen, co‐author of the article, “Creative Ways
To Empower Action To Change the Organization: Cases in Point” was incorrect. He is a Principal with Deloitte
Consulting LLC.
Modulators of membrane drug transporters potentiate the activity of the DMI fungicide oxpoconazole against Botrytis cinerea
Authors: Hayashi Keisuke , Schoonbeek Henk‐jan , De Waard Maarten A
Published: February 2003

Modulators known to reduce multidrug resistance in tumour cells were tested for their potency to synergize the fungitoxic activity of the fungicide oxpoconazole, a sterol demethylation inhibitor (DMI), against Botrytis cinerea Pers. Chlorpromazine, a phenothiazine compound known as a calmodulin antagonist, appeared the most potent compound. Tacrolimus, a macrolide compound with immunosuppressive activity, was also active. The synergism of chlorpromazine negatively correlated with the sensitivity of the parent strain and mutants of B cinerea. The synergism was highest in a mutant that overexpressed the ATP‐binding cassette transporter BcatrD, known to transport DMI fungicides such as oxpoconazole. The synergism of chlorpromazine positively correlated with its potency to enhance the accumulation of oxpoconazole in BcatrD mutants. These results indicate that chlorpromazine is a modulator of BcatrD activity in B cinerea and suggest that mixtures of DMI fungicides with modulators may represent a perspective for the development of new resistance management strategies.

© 2003 Society of Chemical Industry
Evaluation of Erysiphe graminis f sp tritici field isolates for resistance to strobilurin fungicides with different SNP detection systems
Authors: Bäumler Stefan , Sierotzki Helge , Gisi Ulrich , Mohler Volker , Felsenstein Friedrich G , Schwarz Gerhard
Published: February 2003

A single nucleotide polymorphism (snp) in the cytochrome b gene confers resistance to strobilurin fungicides in Erysiphe graminis DC f sp tritici Marchal. On the basis of this point mutation three different types of molecular markers have been developed. Cleaved amplified polymorphic sequences and allele‐specific PCR were used to score resistant and sensitive isolates from specifically selected regional populations across Europe. The results of molecular tests were in total agreement with the resistance phenotypes revealed by in vivo tests. Serial dilutions of mixed samples (resistant/sensitive) delimited the detection for strobilurin‐resistant alleles to a range of 10–50% for both marker classes. Due to these detection limits no mixture of mitochondria within individual isolates was found. Denaturing high performance chromatography was used to increase the detection sensitivity for the mutant allele. Although the detection limit was lowered to 5–10%, there was no evidence for the existence of mixed mitochondrial genotypes.

© 2003 Society of Chemical Industry
A mechanism for the formation of bis‐glutathione conjugates of propargyl alcohol
Authors: Banijamali Ali R , DeMatteo Vincent , Sumner Susan J
Published: February 2003

Our earlier research clearly revealed glutathione (GSH) conjugation as a major pathway for the metabolism of propargyl alcohol (2‐propyn‐1‐ol) in rats and in mice. The identification of the metabolite 3,3‐bis[(2‐acetylamino‐2‐carboxyethyl)thio]‐1‐propanol (I) and its congeners represented the first example of multi‐glutathione addition to a triple bond, and invoked further research to determine the mechanism for bis‐conjugation. To determine whether GSH conjugated directly with propargyl alcohol or after oxidation of the latter to 2‐propynal, urinary metabolites from rats administered deuterium‐labeled propargyl alcohol were characterized. Following TLC separation and HPLC purification, mass spectrometry was used to show a single mass unit increase for metabolite I over that of the chemically synthesized standard. This result indicates that conjugation of propargyl alcohol with GSH to form the bis‐conjugates occurred after initial oxidation to 2‐propynal, a reaction that is analogous to a Michael addition.

© 2003 Society of Chemical Industry
Development and preventative effect against pine wilt disease of a novel liquid formulation of emamectin benzoate
Authors: Takai Kazuya , Suzuki Toshio , Kawazu Kazuyoshi
Published: February 2003

Injection of the poorly water‐soluble emamectin benzoate (EB) into pine trunks required the development of an efficient liquid formulation. For injection into big trees in forests a good rate of injection and a high active content were required. Tests on the viscosity and EB‐solubilizing ability of 14 various solubilizers in diethylene glycol monobutyl ether (DGMBE) led to the selection of Sorpol SM‐100PM as the solubilizer of the formulation. Relationships between the solubilizing ability and amounts of Sorpol SM‐100PM and DGMBE relative to that of EB, and between the concentration of the latter and the viscosity or the injection rate of the formulation led to a novel 40 g litre−1 emamectin benzoate formulation (Shot Wan Liquid Formulation), which was composed of EB (40), Sorpol SM‐100PM (120), DGMBE (160) and distilled water (50 g litre−1) in methanol. Injection of this formulation at a dose of 10 g EB per unit volume of pine tree prevented over 90% of the trees from wilting caused by pine wood nematode, and this preventative effect continued for 3 years. Neither discolouration of the leaves nor injury around the injection hole on the trees was observed after injection of the formulation.

© 2003 Society of Chemical Industry
Adjusting treatment comparisons to account for non‐randomized interventions: an example from an angina trial
Authors: White Ian R. , Carpenter James , Pocock Stuart J. , Henderson Robert A.
Published: February 2003

In a clinical trial where some subjects receive one or more non‐randomized interventions during follow‐up, primary interest is in the effect of the overall treatment strategies as implemented, but it may also be of interest to adjust treatment comparisons for non‐randomized interventions. We consider non‐randomized interventions, especially surgical procedures, which only occur when the outcome would otherwise have been poor. Focusing on an outcome measured repeatedly over time, we describe the variety of questions that may be addressed by an adjusted analysis. The adjusted analyses involve new outcome variables defined in terms of the observed outcomes and the history of non‐randomized intervention. We also show how to check the assumption that the outcome would otherwise have been poor, and how to do a sensitivity analysis. We apply these methods to a clinical trial comparing initial angioplasty with medical management in patients with angina. We find that the initial benefit of a single angioplasty in reducing angina tends to disappear with time, but a policy of additional interventions as required yields a benefit that is maintained over 4 years. Such methods may be of interest to many pragmatic randomized trials in which the effects of the initial randomized treatments and the effects of the overall treatment strategies as implemented are both of interest. Copyright © 2003 John Wiley & Sons, Ltd.
Group sequential design for comparative diagnostic accuracy studies
Authors: Mazumdar Madhu , Liu Aiyi
Published: February 2003

In the field of diagnostic medicine, comparative clinical trials are necessary for assessing the utility of one diagnostic test over another. The area under the receiver operating characteristic (ROC) curve, commonly referred to as AUC, is a general measure of a test's inherent ability to distinguish between patients with and without a condition. Standardized AUC difference is the most frequently used statistic for comparing two diagnostic tests. In therapeutic comparative clinical trials with sequential patient entry, fixed sample design (FSD) is unjustified on ethical and economical grounds and group sequential design (GSD) is frequently used. In this paper, we argue that the same reasoning exists for the comparative clinical trials in diagnostic medicine and hence GSD should be utilized in this field for designing trials. Since computation of the stopping boundaries of GSD and data analysis after a group sequential test rely heavily on Brownian motion approximation, we derive the asymptotic distribution of the standardized AUC difference statistic and point out its resemblance to the Brownian motion. Boundary determination and sample size calculation are then illustrated through an example from a cancer clinical trial. Copyright © 2003 John Wiley & Sons, Ltd.
Controlling type I error rate for fast track drug development programmes
Authors: Shih Weichung J. , Ouyang Peter , Quan Hui , Lin Yong , Michiels Bart , Bijnens Luc
Published: February 2003

The U.S. Food and Drug Administration (FDA) Modernization Act of 1997 has a Section (No. 112) entitled ‘Expediting Study and Approval of Fast Track Drugs’ (the Act). In 1998, the FDA issued a ‘Guidance for Industry: the Fast Track Drug Development Programs’ (the FTDD programmes) to meet the requirement of the Act. The purpose of FTDD programmes is to ‘facilitate the development and expedite the review of new drugs that are intended to treat serious or life‐threatening conditions and that demonstrate the potential to address unmet medical needs’. Since then many health products have reached patients who suffered from AIDS, cancer, osteoporosis, and many other diseases, sooner by utilizing the Fast Track Act and the FTDD programmes. In the meantime several scientific issues have also surfaced when following the FTDD programmes. In this paper we will discuss the concept of two kinds of type I errors, namely, the ‘conditional approval’ and the ‘final approval’ type I errors, and propose statistical methods for controlling them in a new drug submission process. Copyright © 2003 John Wiley & Sons, Ltd.
Pattern mixture models for longitudinal quality of life studies in advanced stage disease
Authors: Pauler Donna K. , McCoy Sheryl , Moinpour Carol
Published: February 2003

Analyses of longitudinal quality of life (QOL) for patients with advanced stage disease are frequently plagued by problems of non‐random drop‐out attributable to deteriorating health and/or death. As an example, Moinpour et al. cite specific challenges which limited their report and assessment of QOL for patients treated for advanced stage colorectal cancer in a clinical trial of several chemotherapeutic regimes performed by the Southwest Oncology Group. A particular source of confusion that arises in studies of advanced stage disease is whether or not to differentiate loss of follow‐up due to death from drop‐out where the patient is still alive but has dropped from the study. In this paper we examine exploratory data techniques for longitudinal QOL data with non‐random missingness due to drop‐out and censorship by death. We propose a pattern mixture model for longitudinal QOL, time of drop‐out and survival, which allows for straightforward implementation of sensitivity analyses and explicit comparisons to the raw data. Our method is illustrated in the context of analysing the data and addressing the challenges posed by Moinpour et al. Copyright © 2003 John Wiley & Sons, Ltd.
Hierarchical Bayesian approaches to phase II trials in diseases with multiple subtypes
Authors: Thall Peter F. , Wathen J. Kyle , Bekele B. Nebiyou , Champlin Richard E. , Baker Laurence H. , Benjamin Robert S.
Published: February 2003

We propose a methodology for conducting phase II clinical trials in settings where the disease is categorized into multiple subtypes. A hierarchical Bayesian model is assumed for treatment effects within the subtypes. The hierarchical model, which is tailored to each particular application, allows treatment effects to differ across subtypes while assuminga priorithat the effects are exchangeable and correlated. Two applications are described. The first is a trial of imatinib for sarcoma in which treatment activity is characterized by a binary indicator of tumour response. The second is a phase II trial of a new preparative regimen for allogeneic bone marrow transplantation in patients with haematologic malignancies, with treatment effect characterized by the mean time from transplant to disease progression or death. The applications illustrate how the hierarchical Bayesian model borrows strength across subtypes. Copyright © 2003 John Wiley & Sons, Ltd.
Do life events have their effect on psychosis by influencing the emotional reactivity to daily life stress?
Authors: MYIN-GERMEYS I. , KRABBENDAM L. , DELESPAUL P. A. E. G. , VAN OS J.
Published: February 2003

Background. Life events (LE) have consistently been found to influence course and outcome of psychotic disorders. However, the mechanism through which they operate is not known. The present study investigated whether LE have their effect by impacting on the emotional sensitivity for daily hassles.

Method. Patients with clinically remitted psychotic illness (N=42) were studied with the Experience Sampling Method (a structured diary technique assessing current context and mood in daily life) to assess: (1) appraised subjective stress related to daily events and activities; and (2) emotional reactivity conceptualized as changes in both negative affect (NA) and positive affect (PA). LE were assessed with the Brown & Harris Life Event and Difficulties Schedule.

Results. Multilevel regression analyses showed that previous exposure to LE influenced the appraised stressfulness of neither daily events nor the activities in which the subjects were involved. However, a history of LE did modify the emotional reaction to daily life stress, both in models predicting NA and in models predicting PA.

Conclusions. By their cumulative effect on emotional reactivity to daily activities and events, LE may render individuals more vulnerable to the onset or persistence of psychotic experiences.
The clinical effectiveness of counselling in primary care: a systematic review and meta-analysis
Authors: BOWER P. , ROWLAND N. , HARDY R.
Published: February 2003

Background. Counselling is frequently used in the management of common mental disorders (such as anxiety and depression) in primary care. However, there are concerns over the clinical effectiveness of counselling, both in comparison with usual general practitioner care, and with other treatments such as alternative psychological therapies and antidepressant treatment. This study used systematic review methodology to assess the current evidence-base.

Method. A systematic literature review located seven trials of relevance, comparing counselling with usual general practitioner care, cognitive-behaviour therapy and antidepressant medication. Data on internal and external validity were examined using a standardized quality rating scheme. Data concerning the impact of counselling on symptoms of anxiety and depression were pooled using meta-analytical procedures.

Results. The main analyses showed significantly greater clinical effectiveness of counselling compared with usual general practitioner care in the short-term (standardized mean difference −0·28, 95% CI −0·43 to −0·13, N=741, six trials) but not the long-term (standardized mean difference −0·07, 95% CI −0·26 to 0·12, N=447, four trials). Sensitivity analyses were undertaken to test the robustness of the results.

Conclusion. Counselling is associated with modest improvement in short-term outcome compared with usual general practitioner care, and thus may be a useful addition to mental health services in primary care.
Patient–practitioner agreement: does it matter?
Authors: GABBAY M. , SHIELS C. , BOWER P. , SIBBALD B. , KING M. , WARD E.
Published: February 2003

Background. Good communication is a crucial clinical skill. Previous research demonstrated better clinical outcomes when practitioners and patients agree about the nature of patients' core presenting complaints. We investigated the nature of this agreement and its impact on outcome among depressed primary care patients.

Method. We compared presenting problem formulations completed by patients, GPs and therapists in a primary care randomized controlled trial of cognitive-behavioural therapy and non-directive counselling for depression. Participants compiled formulations from a list of 13 potential problems of self-completed questionnaires. Subjects scored at least 14 on the Beck Depression Inventory (BDI) at baseline. Outcome measure for this study included BDI at 4 and 12 months, failure to attend for therapy when referred, dropout from therapy and patient satisfaction.

Results. Among 464 trial patients, 395 received therapy. Patient baseline problem formulations included significantly more items than GPs, who identified significantly more items than therapists. Agreement levels varied according to a range of patient and professional variables. While patients in complete agreement with their therapists about their main problem after assessment had lower average BDI scores at 12 months (9·7 v. 12·8, P=0·03); we found no other significant associations between the extent of agreement and clinical outcome. There were significant (but relatively weak) associations between agreement and aspects of patient satisfaction.

Conclusion. Our results suggest that detailed mutual understanding of the presenting complaints may be less important than agreement that the core problem is psychological, and that referral for psychological therapy is appropriate.
Learning disability and epilepsy in an epidemiological sample of individuals with tuberous sclerosis complex
Authors: JOINSON C. , O'CALLAGHAN F. J. , OSBORNE J. P. , MARTYN C. , HARRIS T. , BOLTON P. F.
Published: February 2003

Background. Intellectual impairments are a recognized feature of tuberous sclerosis complex (TSC), but the frequency and degree of intellectual impairments has not been systematically studied in large epidemiological samples using standardized measures. As such, the form of the IQ distribution (uni- or bi-modal) has not been established and the relationship between IQ and other features (e.g. epilepsy history) is poorly delineated. To address these shortcomings, we assessed the intellectual abilities of a large epidemiological sample of individuals with TSC, drawn from the ‘Wessex’ area of SW England and compared them with the abilities of their unaffected siblings.

Method. Standardized tests were used to estimate the abilities of 108 (56 males, 52 females, median age=25, range=4–75) individuals with TSC and 29 unaffected siblings (14 males, 15 females, median age=18, range=6–55). Seizure history was obtained from informants and medical records.

Results. Estimated IQ was bi-modally distributed: 55·5% had an IQ in the normal range; 14% had mild to severe impairments; and 30·5% had profound disability (IQ<21). Forty-four per cent of the individuals with TSC had an IQ<70. In the subset of normally intelligent individuals with TSC, IQ was normally distributed with a mean of 93·6. This mean was significantly lower than the mean IQ of unaffected siblings (IQ=105·6). All individuals with learning disability had a history of seizures that usually commenced before 12 months of age and that often presented as infantile spasms. Multivariate analyses indicated that a history of seizures as well as a history of infantile spasms was predictive of the degree of intellectual impairment.

Conclusions. Intellectual abilities were bi-modally distributed in a representative sample of individuals with TSC. The likelihood of impairment was associated with a history of seizures, particularly infantile spasms. The genetic and brain basis of these findings requires further investigation.
To the Editor
Authors: FISHBAIN DAVID A.
Published: February 2003

In a recent interesting report Barraclough & Harris
(32, 577–584) studied the epidemiology of murder–suicide in
England and Wales.
Computerized, interactive, multimedia cognitive-behavioural program for anxiety and depression in general practice
Authors: PROUDFOOT J. , GOLDBERG D. , MANN A. , EVERITT B. , MARKS I. , GRAY J. A.
Published: February 2003

Background. Cognitive-behavioural therapy (CBT) brings about significant clinical improvement in anxiety and depression, but therapists are in short supply. We report the first phase of a randomized controlled trial of an interactive multimedia program of cognitive-behavioural techniques, Beating the Blues™ (BtB), in the treatment of patients in general practice with anxiety, depression or mixed anxiety/depression.

Method. One hundred and sixty-seven adults suffering from anxiety and/or depression and not receiving any form of psychological treatment or counselling were randomly allocated to receive, with or without medication, BtB or treatment as usual (TAU). Measures were taken on five occasions: prior to treatment, 2 months later, and at 1, 3 and 6 months follow-up using the Beck Depression Inventory, Beck Anxiety Inventory and Work and Social Adjustment Scale.

Results. Patients who received BtB showed significantly greater improvement in depression and anxiety compared to TAU by the end of treatment (2 months) and to 6 months follow-up. Symptom reduction was paralleled by improvement in work and social adjustment. There were no interactions of BtB with concomitant pharmacotherapy or duration of illness, but evidence, on the Beck Anxiety Inventory only, of interaction with primary care practice. Importantly, there was no interaction between the effects of BtB and baseline severity of depression, from which we conclude that the effects of the computer program are independent of starting level of depression.

Conclusions. These results demonstrate that computerized interactive multimedia cognitive-behavioural techniques under minimal clinical supervision can bring about improvements in depression and anxiety, as well as in work and social adjustment, with and without pharmacotherapy and in patients with pre-treatment illness of durations greater or less than 6 months. Thus, our results indicate that wider dissemination of cognitive-behavioural techniques is possible for patients suffering from anxiety and/or depression.
Applied-field molecular dynamics study of a model calcium channel selectivity filter
Authors: Yang Yan , Henderson Douglas , Busath David
Published: February 2003

The calcium channel is thought to have a short selectivity filter containing charged glutamate side chains. This filter was modeled using an atomistic cylinder of length 10 Å in which were confined eight half-charged oxygen anions representing glutamate carboxylate oxygens. Current flow through the filter was computed using applied field nonequilibrium molecular dynamics simulations at various mole fractions of Na+ and Ca2+ in 2 M chloride solutions with simple point charge/extended model water. The filter was cation selective and had conductances in the range of those extrapolated from experimental results. For this model, unlike implicit solvent models at lower voltages and concentrations, the mole fraction behavior was not anomalous and cation binding was nonselective at 2.2 V. Perturbations of filter diameter and confined charge resulted in similar behaviors. At physiological voltages, mole fraction conductance behavior could not be reliably simulated in 100 ns runs, but nonselective cation binding persisted. Nevertheless, it is of interest that ion entry into the confinement region was limited by an energy barrier and at least, in the case of Ca2+, led to an increase in the energy of the other Ca2+ ion in the confinement region and prompt exit of one of them. The filter was most commonly occupied by 2 or 3 Na+ ions in pure Na+ solutions or 1 or 2 Ca2+ ions in pure Ca2+ solutions. For CaCl2 solution, the additional ion, if present, was most commonly stalled behind the entry barrier, i.e., within the channel filter but not yet having entered the confinement region. Thus, the simulations demonstrate the concept that entry of a new mobile Ca2+ ion into the selectivity filter serves to release the prior occupant that was tightly bound.
The influence of embedded atoms, molecules, and clusters on the lifetimes of electron bubbles in large He4 droplets
Authors: Fárnı́k Michal , Toennies J. Peter
Published: February 2003

The lifetimes of electrons injected into large (≈106 atoms) superfluid He4 droplets have been measured in the presence of different prior embedded rare gas atoms, their clusters, and the molecules O2, H2O, and SF6. For the light rare gas atoms Ne and Ar the lifetimes of about 6⋅10−2 s, found previously for pure droplets, are reduced to between 1–2⋅10−2 s. Single molecules with large electron affinities, such as SF6 and O2 and small clusters of H2O lead to a significant increase in the lifetimes. In the case of Kr and Xe, larger clusters with n̄>14 are needed before the lifetimes increase. A simple model, which takes account of the energy levels occupied by the electrons in the corresponding molecules or the clusters, assumed to be solid, can qualitatively explain the observations.
Cavities in ionic liquids
Authors: Bresme Fernando , Alejandre José
Published: February 2003

The formation of cavities in ionic liquids in the vicinity of the liquid binodal curve is investigated by means of Monte Carlo simulations of the restricted primitive model (RPM). Analysis of the cavity size distribution functions provides a quantitative view of the hole sizes arising in ionic liquids when approaching the coexistence region. Cavities of sizes 0.1–1 nm are formed, the larger cavities being favored by the Coulombic forces. The mean cavity size grows with the square root of the temperature. We compute the reversible work needed to create a cavity in the ionic liquid and it is used to estimate the surface tension of the ionic liquid–vapor interface. The accuracy of theoretical approaches based on the scaled particle theory and Ornstein–Zernike equation to estimate the cavity work of formation in ionic liquids is discussed. We find that both simulations and integral equations predict density depletion with increasing cavity size, suggesting the existence of surface drying in ionic liquids.
Selective and reversible entrapment of He and Ne in NaA zeolite at atmospheric pressure
Authors: Saig A. , Danon A. , Finkelstein Y. , Koresh J. E.
Published: February 2003

The He(Ne)/NaA-zeolite system was studied using temperature programmed desorption mass spectrometry (TPD-MS) with a supersonic molecular-beam inlet. Controllable, stable, and reversible entrapment of He and Ne by the β cages of NaA zeolite was experimentally achieved at ambient pressure and around 200 °C. Decapsulation of either He or Ne from NaA is shown to be of a doublet character, indicating on the occurrence of effectively two classes of β cavities: completely blocked cages, never previously observed, and partly blocked ones. The encapsulation of Ne and He in NaA is associated with the coupling of two reversible mechanisms governing the effective free aperture dimension, i.e., apertures thermal dilation and activated ion mobility. Characteristic admission temperatures between 130 °C and 200 °C, show highly selective sieving effect between He and Ne, suggesting its potential utilization for gas separation via a temperature swing practice and for a possible experimental realization of quantum sieving.
Cu(I)-2,9-dimethyl-1,10-phenanthroline: Density functional study of the structure, vibrational force-field, and excited electronic states
Authors: Zgierski Marek Z.
Published: February 2003

Nonlocal hybrid density functional theory method is used to study the structure and force field of the copper(I)–diphenanthroline cation. It is demonstrated that it possesses D2d symmetry in the S0 state, however, deformations to D2 symmetry with rotated phenanthroline rings are not costly energetically and, in fact, such D2 structure is the minimum of the T1 state. Time-dependent DFT method is utilized to calculate the excited electronic states and the visible and UV absorption spectrum. It is shown that the S3 state of B2 symmetry and of metal-to-ligand charge transfer (MLCT) character, is responsible for the ca. 470 nm visible absorption band, while dipole transitions to the S1 and S2 states are symmetry forbidden. We find four triplet electronic states closely spaced and lying just below the S1 state. The ordering and spacing of the lowest triplet and singlet excited states nicely explains the properties of the observed photoluminescence. The calculated maximum of photoluminescence of 759 nm is in a good agreement with the experiment (ca. 730 nm).
Analytic ab initio determination of the IR intensities in stereoregular polymers
Authors: Jacquemin Denis , André Jean-Marie , Champagne Benoı̂t
Published: February 2003

An original scheme is developed to compute, fully analytically, the Hartree–Fock infrared intensities of stereoregular polymers. The infrared intensities are proportional to derivatives of the dipole moment with respect to atomic displacements. For the longitudinal component, the calculation of the infrared intensities requires a specific crystal-orbital treatment. Our approach is based upon the Bishop, Gu and Kirtman method for obtaining the undifferentiated dipole moment [J. Chem. Phys. 114, 7633 (2001)]. The implementation scheme is described in detail. The numerical stability of the methodology is tested on five polymers: (LiH)n, (FH)n, (H2O)n, polymethineimine (CH=N)n and polyacetylene (CH=CH)n. When a proper integration scheme is chosen, the values of the infrared intensities are in perfect agreement with the numerical derivatives of the dipole moment as well as with long oligomer calculations. We apply our approach to the analytical calculation of the vibrational polarizability of two systems.
Migration of holes: Formalism, mechanisms, and illustrative applications
Authors: Breidbach J. , Cederbaum L. S.
Published: February 2003

A hole created in a system, for instance by ionization, can migrate through the system solely driven by electron correlation. The theory describing this migration is derived and cast into a form amenable to ab initio calculations. Three different basic mechanisms of hole migration are presented and analyzed. The results of ab initio calculations on hole migration in realistic systems are discussed. In all cases studied the migration is ultrafast.
Metal and ligand hyperfine couplings in transition metal complexes: The effect of spin–orbit coupling as studied by coupled perturbed Kohn–Sham theory
Authors: Neese Frank
Published: February 2003

The derivation, implementation, and validation of a method to calculate spin–orbit coupling (SOC) contributions to the hyperfine coupling (HFC) is reported. Due to this development it is now possible to calculate the complete ligand and metal nuclei HFCs at a consistent level of theory, i.e., spin unrestricted Hartree–Fock (HF) or density functional theory (DFT). The SOC contributions to the HFC are calculated as a second-order property and are treated by a coupled-perturbed HF or Kohn–Sham treatment. The method is applied to a representative collection of first row transition metal complexes. The calculated metal HFCs are in reasonable to good agreement with the experimental data, with the main error being probably due to the Fermi contact term that is not well represented by present day DFT functionals. Similarities and differences to the closely related field of electronic g-tensor calculations are discussed.
Contrasting origins of the isomerization barriers for vinylidene, fluorovinylidene, and difluorovinylidene
Authors: Loh Zhi-Heng , Field Robert W.
Published: February 2003

The origins of the isomerization barriers for the isomerization of vinylidene (H2C=C), fluorovinylidene (HFC=C), and difluorovinylidene (F2C=C) to their respective acetylenes are explored in this paper. The bonding interactions present in the transition states of each isomerization pathway are analyzed within the framework of electron density deformations and the atoms-in-molecules method using densities obtained from quadratic configuration interaction calculations. The high isomerization barrier for F2C=C is a consequence of the large energetic penalty associated with the C–F bond cleavage to give a covalently unbound fluorine in the transition state. In the case of H2C=C isomerization, analysis by the atoms-in-molecules method reveals that a strong covalent bond exists between the migrating hydrogen and the C=C bond critical point. Concerted C–H bond cleavage and formation in the hydrogen migration process is expected to yield a low energetic requirement for H2C=C isomerization. The observed difference in the bonding interactions present in the transition states for fluorine and hydrogen atom migration can be rationalized in terms of the difference in directionality of the hybrid orbital on the migrating atom. Calculations carried out for both fluorine and hydrogen migration in HFC=C revealed bonding interactions in the transition states that are reminiscent of those observed in the isomerization of F2C=C and H2C=C. An alternative account for the observed violation of Hammond’s postulate in the H2C=C isomerization pathway is also provided. Finally, we demonstrate that the conceptual framework defined in this work may be used to explain the kinetic stabilities of other species that can undergo 1,2-atom shift reactions across an unsaturated bond.
The diagonal Born–Oppenheimer correction beyond the Hartree–Fock approximation
Authors: Valeev Edward F. , Sherrill C. David
Published: February 2003

We report on evaluation of the diagonal Born–Oppenheimer correction (DBOC) to the electronic energy with Hartree–Fock (HF) and conventional correlated wave functions for general molecular systems. Convergence of both HF and configuration interaction (CI) DBOC with the one-particle basis seems to be rather fast, with triple-ζ quality correlation consistent sets of Dunning et al. sufficiently complete to approach the respective basis set limits for the DBOC of the ground state of H2 within 0.1 cm−1. Introduction of electron correlation via the CI singles and doubles method has a substantial effect on the absolute value of the DBOC for H2, H2O, and BH in their ground states (ca. +13 cm−1 out of 115 cm−1, +22 cm−1 out of 622 cm−1, and +11 cm−1 out of 370 cm−1, respectively). The effect of the correlation correction to the DBOC on relative energies is small, e.g., the barrier to linearity of water changes by ca. 1 cm−1; however, the value is difficult to converge to the ab initio limit. Based on recent results by Schwenke [J. Phys. Chem. A 105, 2352 (2001)] and our findings, we expect the correlation correction to the DBOC to have a substantial effect on spectroscopic properties of the ground state of water. The effect of DBOC on equilibrium bond distance re and harmonic vibrational frequency ωe of the ground state of BH is +0.0007 Å and −2 cm−1, respectively. Surprisingly, the former is a much larger change than expected, and greater than errors due to residual incompleteness of electron correlation treatment and basis set in state-of-the-art conventional Born–Oppenheimer computations. The effect of using a correlated wave function for the DBOC evaluation on the above corrections to re and ωe is small.
Comparison of the intermolecular properties of N2…HArF with N2…HF
Authors: McDowell Sean A. C.
Published: February 2003

An ab initio computational study of the properties of a weakly bound complex formed between the recently discovered argon-containing compound HArF and N2 was undertaken at the MP2/6-311G** level of theory. The complex N2…HArF was found to have a zero-point vibrational energy corrected binding energy of 396 cm−1 with respect to the monomer subunits. This complex exhibits a large harmonic vibrational frequency blue shift of 195 cm−1 for the Ar–H stretching vibration mode with a diminished infrared intensity for this mode on formation of the complex. This surprising result prompted a study to understand the source of the blue shift and the results were compared with corresponding computations for the N2…HF complex, which has the same proton acceptor but which shows the usual red shift of the H–F stretching mode.
The constant-volume heat capacity of near-critical fluids with long-range interactions: A discussion of different Monte Carlo estimates
Authors: Daub Christopher D. , Camp Philip J. , Patey G. N.
Published: February 2003

The constant-volume heat capacities, CV, of various near-critical fluids with long-range potentials have been obtained using both canonical and grand-canonical Monte Carlo (GCMC) calculations. In the case of the restricted primitive model it is shown that the large discrepancies between previously reported results arise from the use of different simulation ensembles. In order to investigate how well the different ensemble estimates of CV obtained with small systems can indicate the universality class of the bulk fluid, calculations have been performed for fluids with attractive pair interactions which vary like −1/ra, with a=6, 4, and 3.1. For a=6, Ising-type criticality is expected, while for a=4 and 3.1 the criticality is mean-field. For each of these models the canonical-ensemble estimates of CV do not provide unambiguous confirmation of the expected critical behavior, and hence this is not a reliable method for determining the universality class. This is also true of the GCMC estimates of CV, which appear consistent with Ising-type behavior for all of the systems studied, even for those which are known to exhibit mean-field criticality in the thermodynamic limit. We suggest that these are artifacts associated with finite system size, and we speculate as to why they appear in canonical and GCMC calculations.
Thermal effects and in-plane magnetic anisotropy in thin-film recording media
Authors: Ajan Antony , Abarra E. N. , Acharya B. R. , Inomata A. , Okamoto I. , Shinohara M.
Published: February 2003

The effect of thermal activation on the in-plane magnetic anisotropy [measured as orientation ratio (OR)] of granular longitudinal magnetic recording media is investigated. Temperature and time dependent studies were made on media with different magnetic layer thicknesses. We find that OR is independent of temperature for a stable medium but shows a large increase with temperature for thermally unstable media. At low temperatures and high field sweep rates, the OR values are found to be the same, independent of the magnetic layer thickness. The unique value when thermal activation is reduced is consistent with the high population of the cobalt c axes along the texturing direction as the origin of anisotropy.
Transport properties of carrier-injected DNA
Authors: Shigematsu Taishi , Shimotani Kei , Manabe Chikara , Watanabe Hiroyuki , Shimizu Masaaki
Published: February 2003

We have studied electric properties of carrier-injected deoxyribonucleic acid (DNA) molecules. First, a current (ICA) through a single DNA molecule was measured by the two-probe dc method with varying a distance between a cathode and an anode (dCA). The ICA–dCA curve showed that the current rapidly decreased with increasing dCA (ICA≲0.1 nA for dCA≳6 nm) according to a hopping model. Next, we measured electric properties of DNA injected carriers by two methods; a field effect transistor (FET) arrangement and a chemical doping. In the FET arrangement, we set three electrodes on a single DNA molecule as source, drain, and gate electrodes with a source–drain distance (dDS)∼20 nm. When a voltage was applied to the gate, the source–drain current (IDS) could be detected to be 0.5–2 nA. This showed that charge injection with the FET arrangement would yield a carrier transportation through DNA at least dDS∼20 nm. In order to flow a current through DNA over a distance ∼100 μm, we synthesized the DNA-acceptor cross-linked derivatives (DACD). In the structure of DACD, DNA molecules, which were attached acceptor molecules at guanine sites specifically, were cross-linked by linker molecules. We can modulate the carrier concentration in DACD with changing a guanine–cytosine pair content (pGC) in a DNA double strand. We measured the current–voltage curves of DACD for various pGC. The conductivity of DACD increased nonlinearly with an increase in pGC. We explained this behavior using a percolation model, so that a two-dimensional conductive network would form in DACD.
Influence of microscopic interactions on the spectra of polyacetylene
Authors: Canales Manel , Sesé Gemma
Published: February 2003

The influence of interatomic forces on the spectra of polyacetylene has been analyzed in detail by means of molecular dynamics simulations. Several simulations have been undertaken in which different terms have been added to the force field. Stretching, bending, torsional, and nonbonded forces have been subsequently incorporated in the simulations, in order to point out the specific spectral effects of every interaction. It has been obtained that the influence of all interatomic forces is qualitatively the same in both the trans and cis systems except for the torsions involving hydrogen atoms, which are relevant for the spectra parallel to the chain axis in the cis system, but not in the trans. Stretching and bending forces have a strong influence on the spectra parallel to the chain axis. The interchain forces do not significantly affect any of the spectra. Moreover, the results obtained in our simulations have been used to assign the experimental frequencies of polyacetylene to particular microscopic interactions.
Structure space of model proteins: A principal component analysis
Authors: Yahyanejad Mehdi , Kardar Mehran , Tang Chao
Published: February 2003

We study the space of all compact structures on a two-dimensional square lattice of size N=6×6. Each structure is mapped onto a vector in N-dimensions according to a hydrophobic model. Previous work has shown that the designabilities of structures are closely related to the distribution of the structure vectors in the N-dimensional space, with highly designable structures predominantly found in low density regions. We use principal component analysis to probe and characterize the distribution of structure vectors, and find a nonuniform density with a single peak. Interestingly, the principal axes of this peak are almost aligned with Fourier eigenvectors, and the corresponding Fourier eigenvalues go to zero continuously at the wave-number for alternating patterns (q=π). These observations provide a stepping stone for an analytic description of the distribution of structural points, and open the possibility of estimating designabilities of realistic structures by simply Fourier transforming the hydrophobicities of the corresponding sequences.
A method for evaluating multicanonical potential function without iterative refinement: Application to conformational sampling of a globular protein in water
Authors: Terada Tohru , Matsuo Yo , Kidera Akinori
Published: February 2003

Multicanonical molecular dynamics (MD) is a powerful technique for sampling conformations in rugged potential surfaces, and has been applied to various systems. However, because of the practical difficulty in the iterative refinement of the multicanonical potential function, Emc, a multicanonical MD has not yet been applied to a large system such as a globular protein in explicit solvent. We propose a method to evaluate Emc for a protein in water without the iterative refinement process. The method was applied to the system of a protein, chymotrypsin inhibitor 2 (Ci2), in explicit water, composed of 11 330 atoms. We successfully produced a flat energy distribution covering the energy range corresponding to temperatures from 290 to 400 K. A 10-ns trajectory of the multicanonical MD simulation revealed that Ci2 adopts three different conformations in the long loop (residues 54–63), whereas a 10-ns trajectory of the conventional canonical MD simulation found only one conformation near the initial structure. These results indicate that a multicanonical MD with the method of evaluating Emc is an efficient tool for enhancing the conformational sampling of the native structures of a protein in solution.
On the first-order mean spherical approximation
Authors: Tang Yiping
Published: February 2003

The general solution of the Ornstein–Zernike equation presented by Tang and Lu [J. Chem. Phys. 99, 9828 (1993)] is further discussed. By applying the Hilbert transform, the first-order factorization and direct correlation functions (DCF) are generally and analytically obtained, with emphasis on the mean spherical approximation (MSA) for Yukawa fluids. These analytical results are employed to produce a new DCF for hard spheres through integrating with the previous generalized mean spherical approximation [J. Chem. Phys. 103, 7463 (1995)]. The new DCF is of simple analytical form and remedies the deficiencies of its Percus–Yevick version at high densities. Comparisons between the first-order and full MSA solutions are also made. It is shown that the two solutions give very close results for thermodynamic properties in the phase stable region and phase coexistence curves away from the critical point. At unstable states, the first-order MSA looks more advantageous when applications go beyond homogeneous.