bluuebunny/crossref_metadata_2025 huggingface dataset:
Comorbidity and the Concentration of Healthcare Expenditures in Older Patients with Heart Failure
Authors: Zhang James X. , Rathouz Paul J. , Chin Marshall H.
Published: December 2004

OBJECTIVES: To examine comorbidity and concentration of healthcare expenditures in older patients with heart failure (HF) in the Medicare program.

DESIGN: Retrospective analysis of older fee‐for‐service HF patients, using the 1996 Medicare Current Beneficiary Survey and linked Medicare claims.

SETTING: Variety of clinical settings.

PARTICIPANTS: One thousand two hundred sixty‐six older HF patients from a nationally representative survey.

MEASUREMENTS: Medicare expenditure per person and by types of healthcare services, prevalence of comorbid conditions, and multivariate regression on the association between comorbidities and healthcare expenditure.

RESULTS: Medicare spent an average of $16,514 on medical reimbursement for each HF patient in 1996. Eighty‐one percent of patients had one or more comorbid diseases according to a 17‐disease grouping index. The top 20% of HF patients accounted for 63% of total expenditure. Comorbidity was associated with significantly higher Medicare expenditure. HF patients with more‐expensive comorbidities included those with peripheral vascular disease (24% of patients, mean total expenditure $26,954), myocardial infarction (16% of patients, mean total expenditure $29,867), renal disease (8% of patients, mean total expenditure $33,014), and hemiplegia or paraplegia (5% of patients, mean total expenditure $33,234). Diseases and disorders other than heart failure constituted a significant fraction of the causes of inpatient admissions. Comorbid conditions were more likely to be associated with expensive inpatient care, and patients with these diseases were more likely to spend more overall and more on other types of Medicare services including home health aid, skilled nursing facility, and hospice care.

CONCLUSION: Disease management should consider comorbid conditions for improving care and reducing expenditures in older patients with HF.
Diagnosis and Treatment of Osteoporosis in Patients with Vertebral Compression Fractures
Authors: Neuner Joan M. , Zimmer Jennifer K. , Hamel Mary Beth
Published: December 2004

OBJECTIVES: To determine whether patients with vertebral compression fractures are diagnosed with or treated for osteoporosis.

DESIGN: Retrospective cohort study.

SETTING: Two primary care practices in Massachusetts.

PARTICIPANTS: Two hundred six patients with vertebral compression fractures noted on routine radiographs in 1997–1998.

MEASUREMENTS: Percentage of patients diagnosed with osteoporosis and treated with prescription medications (estrogen, bisphosphonates, raloxifene, or calcitonin). Factors associated with missed osteoporosis diagnosis and treatment, including risk factors for osteoporosis, comorbidities, vertebral fracture severity, and processes of care communication were also examined.

RESULTS: The median patient age was 76, 71% of the cohort was female, and 13% of patients had a history of corticosteroid use. Thirty‐eight percent of subjects (46% of women and 19% of men) were diagnosed with osteoporosis and 32% (39% of women and 14% of men) received prescription medications for osteoporosis. Of women who were diagnosed with osteoporosis, 69% received prescription medications. In adjusted analyses women younger than 50 (adjusted odds ratio (AOR) = 0.09; 95% confidence interval (CI) = 0.01–0.71) and 90 and older (AOR = 0.27; 95% CI = 0.08–0.98) were less likely to be diagnosed with osteoporosis, whereas women with a prior hip or radial fracture (AOR = 3.65; 95% CI = 1.28–10.38) or back pain (AOR = 2.84; 95% CI = 1.38–5.85) were more likely to be diagnosed with osteoporosis.

CONCLUSIONS: Physicians frequently did not diagnose osteoporosis in primary care patients with vertebral fractures, missing an important preventive opportunity for patients at high risk for future fractures. Efforts targeted to improving diagnosis of osteoporosis could improve patient care.
Cefotaxime‐Resistant Bacteria Colonizing Older People Admitted to an Acute Care Hospital
Authors: Bonomo Robert A. , Donskey Curtis J. , Blumer Jeffery L. , Hujer Andrea M. , Hoyenm Claudia K. , Jacobs Michael R. , Whalen Christopher C. , Salata Robert A.
Published: December 2004

OBJECTIVES: To determine the frequency of fecal colonization by cefotaxime‐resistant gram‐negative bacilli in older patients living in the community and in long‐term care facilities (LTCFs) admitted to an acute care hospital.

DESIGN: Case‐control, point prevalence study.

SETTING: Hospital.

PARTICIPANTS: One hundred forty‐three patients aged 65 and older.

MEASUREMENTS: Rectal swab cultures, antibiotic drug sensitivity, beta lactamase isolation, and clonal identity.

RESULTS: Of the 190 surveillance cultures obtained from 143 patients, 26 cefotaxime‐resistant gram‐negative isolates from 22 patients were recovered. The prevalence rate of cefotaxime‐resistant isolates on admission was 13.3% (19/143). A logistic regression model using cefotaxime colonization as the dependent variable found that multiple comorbidities, admission to a surgical service, and having a diagnosis of infection on presentation and a transfusion history were factors associated with the presence of colonization. These four clinical items accurately classified 74% of patients colonized. Antibiotic use and nursing home residence were not associated with the presence of colonization by cefotaxime‐resistant organisms. Twelve of the cefotaxime‐resistant isolates (46%) were identified as Pseudomonas aeruginosa, and 14 (54%) were other gram‐negative bacilli. In six of the 14 isolates that were not P. aeruginosa (36%), it was possible to demonstrate the presence of an AmpC β‐lactamase related to the CMY‐2 β‐lactamase, a plasmid‐borne cephalosporinase.

CONCLUSION: These data raise awareness that there are community‐ and LTCF‐dwelling older patients colonized with gram‐negative enteric bacilli resistant to third‐generation cephalosporins on admission to the hospital. The “reservoir of resistant bacteria” in older people is no longer confined to LTCFs.
Comparison of Two Home Care Protocols for Total Joint Replacement
Authors: Weaver Frances M. , Hughes Susan L. , Almagor Orit , Wixson Richard , Manheim Larry , Fulton Bradley , Singer Ruth
Published: December 2004

OBJECTIVES: To examine the effect of a more‐efficient home care protocol to manage total joint replacement (TJR) patients after surgery.

DESIGN: A randomized trial of two home care protocols for TJR management.

SETTING: A hospital‐affiliated home healthcare agency in a large midwestern city.

PARTICIPANTS: Medicare‐eligible individuals undergoing elective total hip or knee replacement surgery (N = 136).

INTERVENTION: A home care protocol that included preoperative home visits by a nurse and a physical therapist and fewer postoperative visits (range of 9–12 visits) to the home than an existing protocol (range of 11–47 visits).

MEASUREMENTS: Functional status, lower extremity functioning, health‐related quality of life, satisfaction with care, and use and cost of healthcare services for 6 months postsurgery.

RESULTS: There were no differences in functional status, health‐related quality of life, or lower extremity functioning by group at 6 months. A marginally significant gain in satisfaction with access to care (P = .059) was found in the intervention group at 6 months. Home healthcare costs were 55% lower for the streamlined group (P < .001). Other costs did not differ significantly by group.

CONCLUSION: TJR patients who received the more‐efficient home care protocol experienced comparable outcomes to those who received the existing protocol. An abbreviated set of home care visits resulted in more‐efficient delivery of care without compromising patient outcomes.
Early Clinical Exposure to Geriatric Medicine in Second‐Year Medical School Students—The McGill Experience
Authors: Duque Gustavo , Gold Susan , Bergman Howard
Published: December 2004

This study examined the effect of a curriculum change on early clinical exposure to geriatrics for second‐year medical students at McGill University and its effects on learning and students' appreciation of geriatrics as a subspecialty. Second‐year medical students (N = 200) were exposed to a change in the curriculum involving the integration of 10 weekly sessions into one integrated week in geriatric medicine. Students participating in 10 weekly sessions were Group 1 and students participating in one integrated week were Group 2. Students rated their rotation using two different scales. The students completed 12‐item questionnaires during their feedback sessions at the end of the 10‐week session experience or the integrated week. The first six items assessed the students' appreciation of their improvement of knowledge in the subject of geriatrics and aging. The second and third part of the survey (questions 7 and 8) included the students' opinions about the quality of the instruction (teaching feedback) and evaluation. Students in Group 2 found their rotation more effective as a learning experience and expressed greater satisfaction with interaction with the tutors, community settings, and multidisciplinary team sessions. Grades obtained on final examinations showed a better and more‐effective acquisition of knowledge by Group 2. The integrated week is a more‐effective learning tool in the early clinical experience for medical students in geriatric medicine than 10 weekly sessions as the first introductory experience to the field of geriatric medicine.
Falling Through the Cracks: Challenges and Opportunities for Improving Transitional Care for Persons with Continuous Complex Care Needs
Authors: Coleman Eric A.
Published: December 2004

Persons with continuous complex care needs frequently require care in multiple settings. During transitions between settings, this population is particularly vulnerable to experiencing poor care quality and problems of care fragmentation. Despite how common these transitions have become, the challenges of improving care transitions have received little attention from policy makers, clinicians, and quality improvement entities. This article begins with a definition of transitional care and then discusses the nature of the problem, its prevalence, manifestations of poorly executed transitions, and potentially remediable barriers. Necessary elements for effective transitions are then presented, followed by promising new directions for quality improvement at the level of the delivery system, information technology, and national health policy. The article concludes with a proposed research agenda designed to advance the science of high‐quality transitional care.
Temporomandibular joint problems and self‐registration of mandibular opening capacity among adults with Ehlers‐Danlos syndrome. A questionnaire study
Authors: Hagberg Catharina , Korpe Lena , Berglund Britta
Published: December 2004

Structured Abstract

Authors – Hagberg C, Korpe L, Berglund B

Objectives – To study maximal mandibular opening capacity and the prevalence of temporomandibular joint (TMJ) problems reported among a larger group of adults with Ehlers‐Danlos syndrome (EDS). Furthermore, to compare proportions of disorders with those in a cohort of randomized population‐ based controls.

Design – A questionnaire study with self‐registration of maximal mandibular opening capacity.

Setting and Sample Population – One hundred and fourteen persons with EDS and 114 controls in a randomized population‐based cohort.

Experimental variables – Self‐registered maximal mandibular opening capacity values that were calculated from the markings of maximal interincisal distance on spatulas and the assessments of overbite with the aid of photos. Questions concerning EDS, TMJ problems and other related questions.

Outcome Measure – Mean values of maximal mandibular opening capacity compared between groups. Proportions of affirmative answers about TMJ problems compared between persons with EDS and controls who did not have the syndrome.

Results – The EDS persons who reported problems with poor mouth opening capacity when biting into thick pieces of food had a lower mean maximal mandibular opening value compared with the other EDS persons (p < 0.05). The proportions of affirmative answers concerning mobile joints during mouth opening, present TMJ problems, poor mouth opening capacity when biting into thick food, clicking, crepitations and permanent locking were greater compared with the controls (p < 0.05).

Conclusion – These data corroborate the reports in literature that persons with EDS are naturally predisposed to TMJ problems. The self‐registration of maximal mandibular opening capacity was a useful diagnostic tool to provide an objective clinical measure of movement capacity of the TMJ. The clinical measure was in line with the affirmative answers on having problems with poor mouth opening capacity among the EDS persons.
Post‐operative optimization of gum‐chewing kinematics in a prognathic patient
Authors: Yashiro Kohtaro , Takada Kenji
Published: December 2004

Smooth jaw movements during gum chewing, which are defined as those driven by optimally smooth patterns of temporal change in acceleration/deceleration, have been quantified in subjects with acceptable occlusions. This paper reports a case in which significant improvement of the smoothness of masticatory jaw movement was observed following surgical‐orthodontic treatment. A patient, who demonstrated a mandibular prognathism, underwent the treatment. The irregularity in acceleration/deceleration of jaw closing movement during gum chewing was quantified by the movement jerk‐cost, where the jerk is rate of change in movement acceleration/deceleration. The normalized jerk‐costs and results of maximum‐smoothness model simulation were compared between jaw movements at pre‐ and post‐treatment stages. The correction of mandibular prognathism and crossbite allowed the patient to close the jaw with wider lateral excursion. Furthermore, smoothness of the jaw closing movements increased significantly and the velocity profile was characterized as similar to that predicted by the kinematic model after treatment. These findings for achievement of ‘functional occlusion’ that allows the patient to perform smooth and economical jaw closing movements during chewing demonstrate necessity of orthodontic treatment of mandibular prognathism to improve jaw motor function.
Auricular anthropometry of Hong Kong Chinese babies
Authors: Fok T.F. , Hon K.L. , So H.K. , Ng P.C. , Wong E. , Lee A.K.Y. , Chang A.
Published: December 2004

Structured Abstract

Authors – Fok TF, Hon KL, So HK, Wong E, Ng PC, Lee AKY, Chang A

Objectives – To provide a database of the auricular measurements of Chinese infants born in Hong Kong.

Design – Prospective cross‐sectional study.

Setting and Sample Population – A total of 2384 healthy singleton, born consecutively at the Prince of Wales Hospital and the Union Hospital from October 1998 to September 2000, were included in the study. The range of gestation was 33–42 weeks.

Measurements and Results – Measurements included ear width (EW), ear length (EL) and ear position (EP). The data show generally higher values for males in the parameters measured. When compared with previously published data for Caucasian and Jordanian term babies, Chinese babies have shorter EL. The ears were within normal position in nearly all our infants.

Conclusion – The human ear appears to grow in a remarkably constant fashion. This study establishes the first set of gestational age–specific standard of the ear parameters for Chinese new‐borns, potentially enabling early syndromal diagnosis. There are significant inter‐racial differences in these ear parameters.
Wall Effects in Shock Tube Flow
Authors: Emrich Raymond J. , Wheeler Donald B.
Published: December 2004

In order to study wall effects in shock tube flows, measurements have been made of shock strength, of average density across the tube, and of pressure at the walls. These measurements are compared with explicit predictions of Trimpi and Cohen and of Mirels and Braun. Under conditions where the theories should apply, they predict shock attenuation and values of the flow variables sufficiently well to justify as essentially correct the assumptions that the turbulent boundary layer produced by the shock is similar to the boundary layer observed in steady flows and that waves generated by wall effects can be considered as one-dimensional. A need for some modification of the theories is indicated, however, by lack of quantitative agreement in certain cases. Considerable mixing of the hot and cold gases is observed to occur. Neither theory attempts to explain the mixing nor takes into account its effects on wave propagation.
On the Theory of the Bubble Chamber
Authors: Seitz Frederick
Published: December 2004

An attempt is made to analyze the factors which determine the operation of the bubble chamber. It is concluded that the majority of bubbles in conventional chambers are nucleated by moderately energetic free electrons produced by the incident particles in Coulomb encounters. Nuclei are displaced too infrequently by Coulomb encounters to account for the observed densities of bubbles. The electrons deposit their kinetic energy in highly localized regions which then are the source of explosions which produce bubbles of greater than critical size in a time of the order of 10−10 or 10−11 sec. The bubbles grow subsequently by evaporation of the fluid. The temperature of the fluid should be sufficiently close to the critical temperature that the energy required to produce the bubble of critical size can be provided by an electron with a range comparable to or less than the diameter of the bubble of critical size. Otherwise the electron will be unable to localize its energy in a sufficiently small volume in any but highly improbable cases. It is also concluded that the viscosity of the liquid plays a very important role in determining the threshold energy for forming a bubble of critical size when it has a value near 1 centipoise or larger.
Hydromagnetic Stability of a Conducting Fluid in a Circular Magnetic Field
Authors: Edmonds Frank N.
Published: December 2004

The theory of viscous flow between two rotating coaxial cylinders as developed by Taylor and Chandrasekhar is extended to the case when the fluid is an electrical conductor and a circular magnetic field (i.e., one whose lines of force are concentric with the cylinder walls) is present. The equations governing marginal stability are derived, and boundary conditions for perfectly conducting cylinders (Fermi boundary conditions) are formulated for two cases when the difference in cylinder radii is small compared to their mean. In the first case, co-rotating cylinders, the underlying characteristic value problem is solved by a variational method developed by Chandrasekhar to show that convective instability rather than oscillatory overstability will occur for realizable magnetic field strengths. In the second case, co-rotating and counter-rotating cylinders, the underlying characteristic value problem is solved by an expansion in orthogonal functions method developed by Chandrasekhar to determine critical Taylor numbers for marginal stability. The magnetic field inhibits the onset of instability, but this effect is quite small as the hydromagnetic interaction involves displacement but not distortion of the magnetic lines of force.
On the Diffusion of a Chemically Reactive Species in a Laminar Boundary Layer Flow
Authors: Chambré Paul L. , Young Jonathan D.
Published: December 2004

A chemically reactive species is emitted from the surface of a body located in a hydrodynamic flow field. It diffuses into the fluid where it undergoes a simple isothermal, homogeneous transformation. The analysis given enables one to trace the reaction history of this component in a laminar boundary layer flow which develops over the surface of a body.

For illustration the development of a first-order reaction in the neighborhood of a flat plate is calculated. Two reaction types are considered. In one case the reactant is destroyed; in the other, it is generated. The reaction histories show a number of interesting features which are discussed in some detail.
The Copper Oxide Rectifier
Authors: Starr Chauncey
Published: December 2004

The equilibrium diagram of the copper: copper oxide: oxygen system controls the conditions of formation of the cuprous oxide rectifier. The interface between the cuprous oxide and the copper from which it is formed can be studied with polarized light. Intimate contact exists for more than half the total area. The technique of preparing the rectifier has a marked influence on its characteristics. By using a method of measuring the resistance characteristic which did not cause an error due to current heating at the interface, unusual results were obtained from specimens made under various conditions. Measurement of the thermal conductance of the rectifier disclosed a new physical phenomenon, asymmetrical thermal conductance. This asymmetry is in the direction that would be expected from the electron theory of heat conduction.
Surface Tension of Molten Glass
Authors: Pietenpol W. B.
Published: December 2004

The surface tensions of a number of different glasses have been determined by a new method. The method is termed ``The Bulb Method'' and is similar to the soap bubble experiment in which the excess of pressure within the bubble can be balanced against a small head of liquid in a manometer. The weight of the glass bulb is taken into consideration. The method is applicable to a temperature range of approximately 200°C above the annealing point of the glass. The variation of surface tension with change in temperature over the upper range of temperature investigated is found to be of the order of 0.04 dyne per cm per degree C. The magnitude of the surface tension for this range varies from 230 to 360 dynes per cm depending upon the kind of glass. A survey of previous results on surface tension discloses values of widely different magnitudes. One group of experimenters has obtained values of the order of 150 dynes per cm and another group, values of approximately 400 dynes per cm. The results obtained by the bulb method fall approximately midway between the values obtained by previous experimenters.
Permeability of Compacted Powders Determination of Average Pore Size
Authors: Traxler R. N. , Baum L. A. H.
Published: December 2004

With air as the diffusing medium a method and apparatus have been developed for measuring the permeability of compacted, unconsolidated powders. A formula is given for calculating the average pore diameter from the permeability and the percent of voids in the compacted powder. By establishing a simple relationship between the degree of packing, as measured by the percent voids, and the average individual pore diameter it is possible to calculate the pore size in a comminuted solid for any degree of compaction. When liquids (e.g., bitumen, sulfur, etc.) are stabilized by the addition of solid particles, the degree of packing of the particles and the dimensions of the films and masses of liquid separating them exert a profound influence on the consistency of the mixture. Thus, a knowledge of the average pore diameter of a powder as present in a solid-liquid system is of practical value. The influence of average particle size on average pore diameter was studied and data are presented for silica and slate powders.
Rheological Properties of Asphalts III. A Viscosity Index
Authors: Traxler R. N. , Schweyer H. E.
Published: December 2004

A review is given of the work which has been done on the temperature-viscosity relations of bituminous materials and it is pointed out that the methods commonly used for evaluating the changes of consistency with temperature are empirical and unsatisfactory. Viscosity measurements at temperatures ranging from 15° to 35°C have been made on fourteen asphalts of paving consistency by means of the alternating stress method described by Bingham and Stephens. It has been found that for these asphalts and temperatures a plot of the logarithm of viscosity against temperature gives essentially a straight line. An asphalt viscosity index is established which is defined by the relationship: A.V.I.=100(10a−1),where ``a'' is the slope of the log viscosity versus temperature plot. To obtain numerical values for the A.V.I. it is only necessary to determine experimentally the viscosity at two temperatures (in the range where the straight line relation holds) and substitute in the expression: A.V.I.=100[(ηcηd)1/(tc−td)−1],where ηc and ηd are the viscosities (in poises) at tc and td (°C), respectively. This gives the percentage decrease in viscosity of the asphalt for 1°C rise in temperature. The values obtained for the viscosity index for the asphalts studied varied from 19.2 for Venezuelan oil asphalt prepared in a batch steam still to 24.7 for a vacuum reduced Californian oil asphalt.
A Simplified Extrusion Plastometer for Unvulcanized Rubber
Authors: Dillon J. H.
Published: December 2004

A new extrusion plastometer for unvulcanized rubber is described. In this plastometer, the rubber sample is cut automatically and the extrusion chamber is filled in a single operation. The time of extrusion, which is measured by an accurate elapsed time indicator, is chosen as an index of plasticity. The plastometer is shown to be rugged, simple, and rapid in operation. Data are presented which establish the sensitivity and accuracy of the instrument. The results of the extrusion plastometer are discussed with respect to their correlation with those of the Williams plastometer and the United States Rubber Company shearing disk plastometer.
What X-Rays Can Do for Industry
Authors: Hicks Victor
Published: December 2004

X-ray radiography is industrially useful in the physical inspection of welded, cast, or assembled products. X-ray diffraction analysis contributes to the understanding of the details of the processes of manufacturing and treatment of alloys, ceramics, glasses, textiles, and other materials. Both applications have led to the control and improvement of industrial processes and products.
The Dielectric Constant of Air at Radiofrequencies
Authors: Hector L. G. , Schultz H. L.
Published: December 2004

The heterodyne beat frequency method of determining dielectric constants has been applied to the measurement of the dielectric constant of air with an applied frequency of field of 900,000 cycles per second. Radio broadcast signals, stripped of modulation, were used as sources of alternating current of constant high frequency. An electron coupled oscillator was used in the circuit containing the test condenser. Both sources of high frequency were isolated from the detector through buffer stages of amplification. Determination of the beat frequencies was made by photographic recording with a two string oscillograph. A dielectric constant of 1.00058986±0.00000050 is found for air at normal pressure and temperature. This result is in close agreement with the results of other investigators for lower frequencies of applied field and for static measurements.
VIII. The Correlation of the Distillation Range with the Penetration of Creosote into Paper Strips
Authors: Frosch C. J.
Published: December 2004

Measurements of the penetration tensions in paper of a series of creosotes distilled from a single coal tar are reported (the penetration tension being the product of the surface tension and the cosine of the contact angle). It is found that these data conform to two equations: one, previously developed by others from theoretical considerations of the effects of variation in size and distribution of capillary pores upon the theoretical equation of flow, the other, an empirical relationship which is less difficult to apply in more practical problems where many data must be analyzed. The creosote-paper contact angles are shown to be zero or extremely small. Possible errors in the paper strip method are discussed and the importance of calibrating each strip with a reference liquid is demonstrated. The failure of Washburn's equation, which has received considerable attention in the field of fibrous penetration, is shown to be due to the neglect of the hydrostatic head term. The penetration tensions of these creosotes are unaltered by the presence of adsorbed water.
How effective for fold recognition is a potential of mean force that includes relative orientations between contacting residues in proteins?
Authors: Miyazawa Sanzo , Jernigan Robert L.
Published: December 2004

We estimate the statistical distribution of relative orientations between contacting residues from a database of protein structures and evaluate the potential of mean force for relative orientations between contacting residues. Polar angles and Euler angles are used to specify two degrees of directional freedom and three degrees of rotational freedom for the orientation of one residue relative to another in contacting residues, respectively. A local coordinate system affixed to each residue based only on main chain atoms is defined for fold recognition. The number of contacting residue pairs in the database will severely limit the resolution of the statistical distribution of relative orientations, if it is estimated by dividing space into cells and counting samples observed in each cell. To overcome such problems and to evaluate the fully anisotropic distributions of relative orientations as a function of polar and Euler angles, we choose a method in which the observed distribution is represented as a sum of δ functions each of which represents the observed orientation of a contacting residue, and is evaluated as a series expansion of spherical harmonics functions. The sample size limits the frequencies of modes whose expansion coefficients can be reliably estimated. High frequency modes are statistically less reliable than low frequency modes. Each expansion coefficient is separately corrected for the sample size according to suggestions from a Bayesian statistical analysis. As a result, many expansion terms can be utilized to evaluate orientational distributions. Also, unlike other orientational potentials, the uniform distribution is used for a reference distribution in evaluating a potential of mean force for each type of contacting residue pair from its orientational distribution, so that residue-residue orientations can be fully evaluated. It is shown by using decoy sets that the discrimination power of the orientational potential in fold recognition increases by taking account of the Euler angle dependencies and becomes comparable to that of a simple contact potential, and that the total energy potential taken as a simple sum of contact, orientation, and (φ,ψ) potentials performs well to identify the native folds.
X-ray scattering and density-functional theory calculations to study the presence of hydrogen-bonded clusters in liquid N-methylacetamide
Authors: Trabelsi Sahbi , Bahri Mohamed , Nasr Salah
Published: December 2004

A structural investigation of liquid N-methylacetamide (NMA) is performed by x-ray scattering and density functional theory (DFT). Experimental data are analyzed to yield the total structure function SM(Q) and the pair correlation function g(r). The DFT calculations, using the standard triple zeta valence basis set augmented by a diffuse function for carbon, nitrogen and oxygen atoms, are performed on the one hand to study the structure and stability of the two possible conformers cis and trans. On the other hand, they are meant to examine some possible clusters which may describe the intermolecular arrangement in liquid NMA. Among two series of dimers and trimers associations, the spectra are particularly interpreted in terms of: Trans NMA dimers and trimers which resemble the short-range crystal structure, mixed cis and trans trimers and cis cyclic trimers. The H-bonding parameters and the intermolecular energy for each model are described.
First-principles calculations for the cooperative transitions of Yb3+ dimer clusters in Y3Al5O12 and Y2O3 crystals
Authors: Ishii Takugo
Published: December 2004

A first-principles multielectron method is applied to the calculations for the cooperative transitions of trivalent ytterbium ions (Yb3+) in yttrium aluminum garnet (Y3Al5O12; YAG) and yttrium sesquioxide (Y2O3) crystals. The method is based on a molecular-orbital method, in which the overlap between the Yb 4f and the oxygen 2p orbitals is directly considered through a self-consistent procedure. A Yb23+ two-ion model and a (Yb2O14)22− dimer cluster embedded in the point charges of the YAG lattice are compared. The 4f-2p overlaps in the cluster model is needed to explain the cooperative transition probability originating from electric dipole transitions. A (Yb2O10)14− dimer molecule in Y2O3 lattice produces larger electric dipole transition probabilities than the case of YAG. The smaller coordination number in Y2O3 produces the larger 4f-2p overlaps, which result in the larger transition probabilities.
Automated generation of coupled-cluster diagrams: Implementation in the multireference state-specific coupled-cluster approach with the complete-active-space reference
Authors: Lyakh Dmitry I. , Ivanov Vladimir V. , Adamowicz Ludwik
Published: December 2004

An algorithm for generation of the spin-orbital diagrammatic representation, the corresponding algebraical formulas, and the computer code of the coupled-cluster (CC) method with an arbitrary level of the electronic excitations has been developed. The method was implemented in the general case as well as for specific application in the state-specific multireference coupled-cluster theory (SSMRCC) based on the concept of a “formal reference state.” The algorithm was tested in SSMRCC calculations describing dissociation of a single bond and in calculations describing simultaneous dissociation of two single bonds—the problem requiring up to six-particle excitations in the CC operator.
The Huggins band of ozone: Assignment of hot bands
Authors: Zhu H. , Qu Z.-W. , Grebenshchikov S. Yu. , Schinke R. , Malicet J. , Brion J. , Daumont D.
Published: December 2004

The “hot bands” of the Huggins band of ozone are assigned, in both the 218 K and the 295 K spectrum. The assignment is based on intensities calculated with three-dimensional vibrational wave functions for the electronic ground state (X) and the excited state (B). The hot-band structures in the 218 K spectrum all can be assigned to transitions starting from vibrational states with one quantum of stretching excitation in the ground electronic state. The 295 K spectrum shows new structures, which are due to transitions originating from vibrational states in the X state with two quanta of excitation of the stretching modes—despite very small Boltzmann factors. All structures in the low-energy range of the 295 K spectrum, even the very weak ones, thus can be uniquely interpreted. The significance of hot bands results from the strong increase of Franck-Condon factors with excitation of the stretching modes in both the lower and/or the upper electronic states, whose equilibrium bond lengths differ significantly.
Single particle dynamics in ionic liquids of 1-alkyl-3-methylimidazolium cations
Authors: Urahata Sérgio M. , Ribeiro Mauro C. C.
Published: December 2004

Ionic dynamics in room temperature molten salts (ionic liquids) containing 1-alkyl-3-methylimidazolium cations is investigated by molecular-dynamics simulations. Calculations were performed with united atom models, which were used in a previous detailed study of the equilibrium structure of ionic liquids [S. M. Urahata and M. C. C. Ribeiro, J. Chem. Phys. 120, 1855 (2004)]. The models were used in a systematic study of the dependency of several single particle time correlation functions on anion size (F−, Cl−, Br−, and PF6−) and alkyl chain length (1-methyl-, 1-ethyl-, 1-butyl-, and 1-octyl-). Despite of large mass and size of imidazolium cations, they exhibit larger mean-square displacement than anions. A further detailed picture of ionic motions is obtained by using appropriate projections of displacements along the plane or perpendicular to the plane of the imidazolium ring. A clear anisotropy in ionic displacement is revealed, the motion on the ring plane and almost perpendicular to the 1-alkyl chain being the less hindered one. Similar projections were performed on velocity correlation functions, whose spectra were used to relate short time ionic rattling with the corresponding long time diffusive regime. Time correlation functions of cation reorientation and dihedral angles of the alkyl chains are discussed, the latter decaying much faster than the former. A comparative physical picture of time scales for distinct dynamical processes in ionic liquids is provided.
Treating singularities present in the Sutcliffe-Tennyson vibrational Hamiltonian in orthogonal internal coordinates
Authors: Czakó Gábor , Szalay Viktor , Császár Attila G. , Furtenbacher Tibor
Published: December 2004

Two methods are developed, when solving the related time-independent Schrödinger equation (TISE), to cope with the singular terms of the vibrational kinetic energy operator of a triatomic molecule given in orthogonal internal coordinates. The first method provides a mathematically correct treatment of all singular terms. The vibrational eigenfunctions are approximated by linear combinations of functions of a three-dimensional nondirect-product basis, where basis functions are formed by coupling Bessel-DVR functions, where DVR stands for discrete variable representation, depending on distance-type coordinates and Legendre polynomials depending on angle bending. In the second method one of the singular terms related to a distance-type coordinate, deemed to be unimportant for spectroscopic applications, is given no special treatment. Here the basis set is obtained by taking the direct product of a one-dimensional DVR basis with a two-dimensional nondirect-product basis, the latter formed by coupling Bessel-DVR functions and Legendre polynomials. With the basis functions defined, matrix representations of the TISE are set up and solved numerically to obtain the vibrational energy levels of H3+. The numerical calculations show that the first method treating all singularities is computationally inefficient, while the second method treating properly only the singularities having physical importance is quite efficient.
Monte Carlo simulations of segregation in Pt-Ni catalyst nanoparticles
Authors: Wang Guofeng , Van Hove M. A. , Ross P. N. , Baskes M. I.
Published: December 2004

We have investigated the segregation of Pt atoms in the surfaces of Pt-Ni nanoparticles, using modified embedded atom method potentials and the Monte Carlo method. The nanoparticles are constructed with disordered fcc configurations at two fixed overall concentrations (50 at. % Pt and 75 at. % Pt). We use octahedral and cubo-octahedral nanoparticles terminated by {111} and {100} facets to examine the extent of the Pt segregation to the nanoparticle surfaces at T=600 K. The model particles contain between 586 and 4033 atoms (particle size ranging from 2.5 to 5 nm). Our results imply that a complete {100}-facet reconstruction could make the cubo-octahendral Pt-Ni nanoparticles most energetically favorable. We predict that at 600 K due to segregation the equilibrium cubo-octahedral Pt50Ni50 nanoparticles with fewer than 1289 atoms and Pt75Ni25 nanoparticles with fewer than 4033 atoms would achieve a surface-sandwich structure, in which the Pt atoms are enriched in the outermost and third atomic shells while the Ni atoms are enriched in the second atomic shell. We also find that, due to an order-disorder transition, the Pt50Ni50 cubo-octahedral nanoparticles containing more than 2406 atoms would form a core-shell structure with a Pt-enriched surface and a Pt-deficient homogenous core.
Contact forces at the sliding interface: Mixed versus pure model alkane monolayers
Authors: Mikulski Paul T. , Gao Guangtu , Chateauneuf Ginger M. , Harrison Judith A.
Published: December 2004

Classical molecular dynamics simulations of an amorphous carbon tip sliding against monolayers of n-alkane chains are presented. The tribological behavior of tightly packed, pure monolayers composed of chains containing 14 carbon atoms is compared to mixed monolayers that randomly combine equal amounts of 12- and 16-carbon-atom chains. When sliding in the direction of chain cant under repulsive (positive) loads, pure monolayers consistently show lower friction than mixed monolayers. The distribution of contact forces between individual monolayer chain groups and the tip shows pure and mixed monolayers resist tip motion similarly. In contrast, the contact forces “pushing” the tip along differ in the two monolayers. The pure monolayers exhibit a high level of symmetry between resisting and pushing forces which results in a lower net friction. Both systems exhibit a marked friction anisotropy. The contact force distribution changes dramatically as a result of the change in sliding direction, resulting in an increase in friction. Upon continued sliding in the direction perpendicular to chain cant, both types of monolayers are often capable of transitioning to a state where the chains are primarily oriented with the cant along the sliding direction. A large change in the distribution of contact forces and a reduction in friction accompany this transition.
Dependence of line shapes in femtosecond broadband stimulated Raman spectroscopy on pump-probe time delay
Authors: Yoon Sangwoon , McCamant David W. , Kukura Philipp , Mathies Richard A. , Zhang Donghui , Lee Soo-Y.
Published: December 2004

The effect of the time delay between the picosecond Raman pump and the femtosecond Stokes probe pulse on the Raman gain line shape in femtosecond broadband stimulated Raman spectroscopy (FSRS) is presented. Experimental data are obtained for cyclohexane to investigate the dependence of the FSRS line shape on this time delay. Theoretical simulations of the line shapes as a function of the time delay using the coupled wave theory agree well with experimental data, recovering broad line shapes at positive time delays and narrower bands with small Raman loss side wings at negative time delays. The analysis yields the lower bounds of the vibrational dephasing times of 2.0 ps and 0.65 ps for the 802 and 1027 cm−1 modes for cyclohexane, respectively. The theoretical description and simulation using the coupled wave theory are also consistent with the observed Raman gain intensity profile over time delay, reaching the maximum at a slightly negative time delay (∼−1 ps), and show that the coupled wave theory is a good model for describing FSRS.
Theory of torsional non-Condon electron transfer: A generalized spin-boson Hamiltonian and its nonadiabatic limit solution
Authors: Jang Seogjoo , Newton Marshall D.
Published: December 2004

The paper develops a theory of electron transfer with torsionally induced non-Condon (NC) effects. The starting point of the theory is a generalized spin-boson Hamiltonian, where an additional torsional oscillator bilinearly coupled to other bath modes causes a sinusoidal NC modulation. We derive closed form time dependent nonadiabatic rate expressions for both sudden and relaxed initial conditions, which are applicable for general spectral densities and energetic condition. Under the assumption that the torsional motion is not correlated with the polaronic shift of the bath, simple stationary limit rate expression is obtained. Model calculations of this rate expression illustrate the effects of torsional quantization and gating on the driving force and temperature dependences of the electron transfer rate. The classical limit of the rate expression consists of three Marcus-type terms, and is shown to agree very well with the exact numerical result.
Dependence of ion hydration on the sign of the ion’s charge
Authors: Grossfield Alan
Published: December 2004

The solvation of simple ions in water is studied using molecular dynamics simulations with a polarizable force field. Previous simulations using this potential demonstrated that anions are more favorably solvated in water than cations. The present work is an attempt to explain this result by examining the effects of ions on the surrounding water structure, with particular focus on the first solvation shell and its interactions with the surrounding water. We conclude that while the first solvation shell surrounding cations is frustrated by competition between ion-water and water-water interactions, solvation of anions is compatible with good water-water interactions.
Infrared absorption by collisional CH4+X pairs, with X=He, H2, or N2
Authors: Buser Michael , Frommhold Lothar
Published: December 2004

Existing measurements of the collision-induced rototranslational absorption spectra of gaseous mixtures of methane with helium, hydrogen, or nitrogen are compared to theoretical calculations, based on refined multipole-induced and dispersion force-induced dipole moments of the interacting molecular pairs CH4–He, CH4–H2, and CH4–N2. In each case the measured absorption exceeds the calculations substantially at most frequencies. We present the excess absorption spectra, that is the difference of the measured and the calculated profiles, of these supramolecular CH4–X systems at various gas temperatures. The excess absorption spectra of CH4–X pairs differ significantly for each choice of the collision partner X, but show common features (spectral intensities and shape) at frequencies from roughly 200 to 500 cm−1. These excess spectra seem to defy modeling in terms of ad hoc exchange force–induced dipole components attempted earlier. We suggest that besides the dipole components induced by polarization in the electric molecular multipole fields and their gradients, and by exchange and dispersion forces, other dipole induction mechanisms exist in CH4–X complexes that presumably are related to collisional distortion of the CH4 molecular frame.
CH
x
hydrogenation on Co(0001): A density functional theory study
Authors: Gong Xue-Qing , Raval R. , Hu P.
Published: December 2004

Hydrogenation is an important process in the Fischer–Tropsch synthesis. In this work, all the elementary steps of the hydrogenation from C to CH4 are studied on both flat and stepped Co(0001) using density functional theory (DFT). We found that (i) CH3 hydrogenation (CH3+H→CH4) is the most difficult one among all the elementary reactions on both surfaces, possessing barriers of around 1.0 eV; (ii) the other elementary reactions have the barriers below 0.9 eV on the flat and stepped surfaces; (iii) CH2 is the least stable species among all the CHx(x=1–3) species on both surfaces; and (iv) surface restructuring may have little effect on the CHx(x=0–3) hydrogenation. The barriers of each elementary step on both flat and stepped surfaces are similar and energy profiles are also similar. The reason as to why CHx hydrogenation is not structure-sensitive is also discussed.
Phase diagram of a binary symmetric hard-core Yukawa mixture
Authors: Schöll-Paschinger Elisabeth , Levesque Dominique , Weis Jean-Jacques , Kahl Gerhard
Published: December 2004

We assess the accuracy of the self-consistent Ornstein-Zernike approximation for a binary symmetric hard-core Yukawa mixture by comparison with Monte Carlo simulations of the phase diagrams obtained for different choices of the ratio α of the unlike-to-like interactions. In particular, from the results obtained at α=0.75 we find evidence for a critical endpoint in contrast to recent studies based on integral equation and hierarchical reference theories. The variation of the phase diagrams with range of the Yukawa potential is investigated.