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PubMed1988

Vertex representations of quantum affine algebras.

We construct vertex representations of quantum affine algebras of ADE type, which were first introduced in greater generality by Drinfeld and Jimbo. The limiting special case of our construction is the untwisted vertex representation of affine Lie algebras of Frenkel-Kac and Segal. Our representation is given by means of a new type of vertex operator corresponding to the simple roots and satisfying the defining relations. In the case of the quantum affine algebra of type A, we introduce vertex operators corresponding to all the roots and determine their commutation relations. This provides an analogue of a Chevalley basis of the affine Lie algebra [unk](n) in the basic representation.

Journal Article↗

PubMed1992

Axial distances in discrete Möbius groups.

We describe here new lower bounds for the trace of the commutator of a discrete two-generator group of Möbius transformations. These results lead to sharp estimates for the distance between the axes of elliptics in a discrete group and hence to new bounds for the volume of hyperbolic manifolds and orbifolds that will be discussed elsewhere.

Journal Article↗

PubMed1994

Structure of the truncated icosahedron (such as fullerene or viral coatings) and a 60-element conjugacy class in PSl(2, 11).

The proper symmetry group of a truncated icosahedron P is the icosahedral group PSl(2, 5). However, knowing the symmetry group is not enough to specify the graph structure (e.g., the carbon bonds for fullerene, C60) of P. The group PSl(2, 5) is a subgroup of the 660-element group PSl(2, 11). The latter contains a 60-element conjugacy class, say M, of elements of order 11. I show here that M exhibits a model for P where the graph structure is expressed group-theoretically. For example, the 12 pentagons are the maximal commuting subsets of M. Such a model creates the opportunity of using group-based harmonic analysis (e.g., convolution calculus) to deal with problems concerning the truncated icosahedron.

Journal Article↗

PubMed2000

On a classical limit for electronic degrees of freedom that satisfies the Pauli exclusion principle.

Fermions need to satisfy the Pauli exclusion principle: no two can be in the same state. This restriction is most compactly expressed in a second quantization formalism by the requirement that the creation and annihilation operators of the electrons satisfy anticommutation relations. The usual classical limit of quantum mechanics corresponds to creation and annihilation operators that satisfy commutation relations, as for a harmonic oscillator. We discuss a simple classical limit for Fermions. This limit is shown to correspond to an anharmonic oscillator, with just one bound excited state. The vibrational quantum number of this anharmonic oscillator, which is therefore limited to the range 0 to 1, is the classical analog of the quantum mechanical occupancy. This interpretation is also true for Bosons, except that they correspond to a harmonic oscillator so that the occupancy is from 0 up. The formalism is intended to be useful for simulating the behavior of highly correlated Fermionic systems, so the extension to many electron states is also discussed.

Journal Article↗

PubMed2000

Patients or customers: ethical limits of market economy in health care.

There is a move away from a market economy in health care in the United States and a move towards such a market in Germany. This article tries to make explicit what underlies the moral intuition that there is a tension between a market economy and health care. First, health care is analyzed in terms of the economic theory of the market and incompatibilities are described. The moral problem is identified as the danger of liquefying the distinction between persons and things. The basic moral intuition seems to be the classical social contract: as a functioning market is governed by the principle of commutative justice, free riders have to be kept away, which is achieved by coercion that is not provided by the market; coercion can be justified by a social contract. The special moral problems of a social contract for health care are discussed. It is argued that public coercion in order to collect contributions for essential health care is justified.

Delivery of Health Care↗

PubMed2002

Assessing the classification of work-relatedness of fatal incidents: a comparison between Australia, New Zealand and the United States.

As part of a larger study comparing work-related fatal injury of workers in Australia, New Zealand and the United States, an assessment was made of the similarities and differences between the three countries in identifying fatal incidents as work-related or not. The researchers in each country independently classified 333 brief scenarios, describing a variety of fatal incidents, into one of nine categories related to work: worker, bystander, commuter, volunteer, student, suicide, other, unknown and none of the above. Complete agreement with the classification was moderate (62%), but agreement when classifying scenarios as working, not working or unknown was much higher (full agreement for 80% of scenarios; Kappa = 0.71). Only 5% of scenarios were classified differently by all three countries. Other main findings of the study were that there is variation between countries in the interpretation of what is and what is not work-related, and variation in the amount or type of information required to make a definitive classification. Common circumstances described in the scenarios for which there was some disagreement in classification included domestic violence incidents at work, volunteer workers, business trips, social functions connected to work, hobby farmers and some possible bystander incidents that occurred on farms or on the road. The results suggest that, even without the use of standard definitions, comparisons between the datasets of the countries involved in this study can be made with reasonable confidence. However, they also emphasise the importance of minimising ambiguity in the definitions used, and of understanding the manner in which the definitions are applied, when comparing results between studies.

Accidents, Occupational↗

PubMed2003

Ocular kinematics, vergence, and orbital mechanics.

Important aspects of ocular kinematics relate to the geometric configuration of extraocular muscles (EOMs). The orbital layer of each rectus EOM inserts on a connective tissue ring called a pulley that deflects the EOM path. Global layer fibers of each EOM pass through the pulley to insert on the sclera. The orbital layer thus controls linear translation of the pulley, regulating the EOM's pulling direction, while the global layer rotates the eye. The active pulley hypothesis (APH) states that pulleys are actively positioned to regulate ocular kinematics. The coordinated control postulate of the APH proposes that during conjugate visually guided eye movements, rectus pulleys move the same anteroposterior distance as their insertions, but the inferior oblique pulley moves with vertical gaze by half the amount as the inferior rectus insertion. These motions, observable by magnetic resonance imaging (MRI), shift the pulling directions of these EOMs by half the ocular angle, mechanically implementing a 'linear oculomotor plant' appearing mathematically commutative to the brain and consistent with Listing's Law of ocular torsion. In the non-converged state with the head upright and stationary, rectus pulleys move little transverse to the EOM axes. During convergence and during the static torsional vestibulo-ocular reflex, MRI shows that the rectus pulley array rotates around the line of sight. Oblique EOM orbital layers may implement this shift.

Biomechanical Phenomena↗

PubMed2004

The Nordic Trueness Project 2002: use of reference measurement procedure values in a general clinical chemistry survey.

Up to 136 laboratories participated in a joint effort to assess the trueness of routine measurements for 14 serum components. An unmodified, fresh-frozen human serum ("IMEP-17 Material 1"), produced for an international inter-laboratory comparison, served as the "master material". The serum had assigned values of the highest available metrological quality, and is assumed to involve no or negligible commutability problems. The material was used in the assignment of traceable values to two other reference sera, "CAL" and "X", through parallel measurements on the three materials according to a common protocol. In this transfer process, uncertainty estimates were provided for all values. The material CAL had been supplied with reference measurement procedure values in 1997, and the two sets of assigned values agreed well. A lyophilized control serum "HK02" was also included in the routine analysis series. It, too, had assigned values based on reference measurement procedures. Significant matrix effects were found. The project has provided: Assigned traceable values for 14 components in a fresh-frozen serum, available to Nordic laboratories for the coming years as "NFKK reference serum X"; Confirmation of earlier assigned reference measurement procedure values for a number of components in CAL, the main calibrator in the Nordic Reference Interval project (NORIP). The transferred values will now serve as the primary reference.; Evidence of long-term stability ( > or = 5 years) of the fresh-frozen serum CAL when stored at -80 degrees C; Evidence of substantial matrix effects in the processed serum HK02. The findings should be used to discuss to what extent reference measurement procedure values are useful and cost-efficient for this type of material.

Blood Chemical Analysis↗

PubMed2004

Effect of analytical quality on establishing common reference intervals and their use.

In the Nordic Reference Interval Project (NORIP), reference intervals were established for 25 common clinical biochemical quantities. In the project, samples from more than 3000 reference individuals collected in the 102 participating laboratories from all five Nordic countries were analysed locally. In order to maintain a high level of analytical quality and to document this quality, a common calibrator/reference preparation (CAL) and a number of control samples were analysed together with the reference samples. All these materials were serum pools of unprocessed serum from many donors in order to obtain commutable materials. The CAL was used to harmonize the many different analytical procedures and calibrations by simple recalibration by the factor T/M where T is the target value based on reference methods and M is the mean of 10 replicate measurements of CAL in each laboratory. The analytical quality specifications (analytical goals) were based on specifications created directly for the purpose of sharing common reference intervals and only the bias criteria were used because bias is the dominating problem in transfer of reference intervals. These specifications were different for the evaluation of reference values to create common reference intervals and for the laboratories to use these common reference intervals (when established). An interesting outcome was that it was only for the biologically well-regulated quantities serum-sodium and serum-calcium that the selection of the best laboratories gave considerably narrower reference intervals.

Chemistry, Clinical↗

PubMed2004

Nordic Reference Interval Project Bio-bank and Database (NOBIDA): a source for future estimation and retrospective evaluation of reference intervals.

In the Nordic Reference Interval Project 2000 (NORIP) serum, Li-heparin plasma and EDTA buffy coat were collected at 102 laboratories in 5 Nordic countries from healthy individuals aged 18 years or more and evenly distributed for laboratory, gender and age. Multiple aliquots of these samples from each of about 3000 persons are now stored at the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) at a temperature of below -80 degrees C. The commutable NFKK Reference Serum X with certified values traceable to reference methods and measured in NORIP in the same series as the samples is also available from NOBIDA. Data describing the person and the sample conditions are stored together with analytical results and data describing the measurement systems. The bio-bank along with material and data is administered by the NOBIDA committee on behalf of the NFKK (Scandinavian Society of Clinical Chemistry) to be used by Nordic laboratories for any purpose beneficial to the development of clinical biochemistry in general and particularly for creating reference intervals for other biochemical properties than those established by NORIP. Furthermore, research on the already stored information alone is encouraged. Thus colleagues are now welcome to use this extensive material for research and development in clinical biochemistry.

Adolescent↗

PubMed2004

Algorithmic generation of freely jointed hard sphere chains and properties of their inertial tensors.

A statistical algorithm, capable of generating a large number of freely jointed hard sphere chains, is presented. This is the first of a series of algorithms being developed to model unfolded proteins by different modes of hard sphere chains. The aim of these studies is to systematically investigate the effects of different factors, such as atomic radii, bond angles, torsion angles, chain length, etc., on the conformation of unfolded proteins and other random polymers. As continuous models, various types of hard sphere chains enable one to isolate the aforementioned factors one at a time for investigation and thus are advantageous over discrete lattice models. In particular, the freely jointed hard sphere chain model allows one to evaluate the excluded volume effect. As a first step in this endeavor, the average determinant D(N, r) and the average trace T(N, r) of the inertial tensor A of the random chains were calculated at various sphere radii r and chain lengths N. It is found that both the average determinant D(N, r) and the average trace T(N, r) scale linearly with chain length N after logarithmic transformation. However, the critical exponent of D(N, r) increases with r faster than that of T(N, r) as a result of the non-commutativity between the det operator and the average operator < >. The significance of the algorithm and the results obtained on understanding random polypeptide chains are discussed.

Algorithms↗

PubMed2006

Sleep on the job partially compensates for sleep loss in night-shift nurses.

Nursing personnel in Brazil are usually submitted to fixed 12 h shifts with no consecutive working days or nights. Moonlighting is common in this group, with a consequent increase in the number of working hours. The possibility of sleeping on the job during the night shift in the studied hospitals had already been described. The present study aims to analyze whether the time devoted to daily activities (sleep, rest, leisure, housework, commuting, personal needs, care of children or other people, non-paid work, and study) is related to the number of worked hours and to nap-taking during the night shift. The field study took place at two public hospitals in Rio de Janeiro, Brazil. Workers filled out a structured form on time devoted to the above-mentioned activities for at least four consecutive days. The time devoted to sleep was analyzed according to its occurrence at home or on the job. Workers were classified according to the number of jobs (one job/two jobs) and the time dedicated to work according to the median of the whole series (below the median/above the median). All workers who had at least one working night were analyzed as to nap-taking on the job. They were classified according to the sleep occurrence during the night shift-the sleep group and the non-sleep group, both of which were compared to daytime workers. Statistical treatment of data included non-parametrical procedures. The study group comprised 144 workers (mean age: 35.7+/-10.5 years old; 91% women; 78% nurse assistants, the remainder registered nurses). They recorded their daily activities for 4-11 days; 829 cumulative days were analyzed for the whole group. A total of 165 working nights were analyzed; sleep or rest occurred during 112 (68%) of them, with mean sleep/rest duration of 141+/-86 min. Time devoted to sleep and leisure varied according to the number of working hours, being significantly reduced in those submitted to longer work hours (p < 0.001 and p = 0.002, respectively). Results close to significance point to a reduction in the time dedicated to housework among workers with long work hours (p = 0.053). The time spent on sleep/rest per working night did not differ according to the number of worked hours (p = 0.490). A tendency was observed for those who have two jobs to devote more time to sleep/rest on the job (p = 0.058). The time of personal needs was significantly lower among those who did not sleep on the job as compared to day workers (p = 0.036). The total sleep time was significantly lower among those who did not sleep on the job, as compared to day workers and to those who slept on the job (p = 0.004 and p = 0.05, respectively). As to home sleep length, workers who slept and those who did not sleep on the job were similar and slept significantly less than exclusively daytime workers (p < 0.001 and p = 0.002, respectively). Sleeping on the job during the night shift seems to partially compensate for the shorter sleep at home among night workers and may play a beneficial effect in coping with two jobs.

Adult↗

PubMed2002

Availability of emergency contraceptive pills at university and college student health centers.

The author used the stages of change model to determine how ready student health centers at surveyed universities and colleges were to make emergency contraceptive pills (ECPs) available to students. Of the 358 centers that responded, 52.2% offered ECPs and 47.8% did not. The benefits of offering ECPs were listed as pregnancy prevention, the opportunity to introduce students to traditional contraception methods, and students' appreciation. Barriers to offering ECPs included institutions' religious affiliations, clinic and administrative staff objections, inability to prescribe or dispense medications, fear of liability, concern that ECPs would undermine students' use of traditional contraception methods, and no expressed need. Whether ECPs were available was associated with demographic characteristics of the institutions that responded, including geographic region, type of institution, size of student population, and students' status as commuter or on-campus residents.

Adolescent↗

PubMed1991

College health services in California.

College health services are an underrecognized segment of California's health delivery system. Higher education institutions in California vary in their arrangements for the provision of health services. Some of the smaller institutions provide nurse triage, first aid, and referral only, whereas other institutions provide 24-hour-per-day/7-day-per-week comprehensive ambulatory and inpatient services. More than 200 full-time equivalent physicians are employed in college health services in California. Patient profiles served by college health services targeted the traditional college student age range. Some institutions, however, have expanded their services to include nonstudent university employees and their dependents. Comparing numbers of outpatient visits and professional staffing requirements to student enrollment showed significant variability between institutions, depending upon the scope of services provided (basic, intermediate, comprehensive) and the type of student population (residential, commuter, mixed).

Adult↗

PubMed1999

Driver compliance with stop signs at pedestrian crosswalks on a university campus.

Pedestrians on college campuses interact continuously with various motorized vehicles. Rates of compliance with stop signs at pedestrian crosswalks and noncomplying vehicles were monitored in spring 1996 on a large urban campus. The number of pedestrians, pedestrian clearance, type of vehicle, hour of day, and day of week were monitored at 3 pedestrian crosswalks. The overall compliance rate for stop signs was 22.8 per 100 vehicles, ranging from 1.4 per 100 for bicycles to 46.2 per 100 for commuter vans. Compliance increased to 53 per 100 vehicles when pedestrians were present in the crosswalk. Several differences in compliance rates were found among the observation sites. Lowest compliance was observed for bicycles and motorcycles. Pedestrians on this and other college campuses risk injuries because of violations of pedestrian right-of-way laws. The problem calls for appreciable educational efforts by college health personnel.

Automobile Driving↗

PubMed1999

Prevalence of alcohol-use disorders and alcohol-related problems in a college student sample.

Most studies of alcohol consumption patterns and alcohol-related problems among college students have failed to include a diagnostic measure based on Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria. Applying the DSM-IV standards would facilitate an analysis of the prevalence of alcohol-use disorders and individual symptoms of those disorders. A structured diagnostic interview based on DSM-IV criteria (the alcohol section of the Substance Abuse Module) and several alcohol screening instruments were administered to 306 undergraduate students at an urban commuter campus. The prevalence of current and lifetime alcohol-use disorders, individual symptoms of those disorders, and other alcohol-related problems are reported, as well as data regarding alcohol consumption patterns and binge drinking. The data are analyzed in terms of demographic variables, including sex, ethnicity, year in school, age, and marital status of those in the sample.

Adolescent↗

PubMed2004

Biochemistry and clinical role of human cystatin C.

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Cerebrospinal Fluid↗

PubMed1995

Personal and fixed-site ozone measurements with a passive sampler.

Personal exposures to ozone were measured in the summers of 1992 and 1993 in the Fraser Valley, a suburban and rural river valley bordering the metropolitan region of Vancouver, British Columbia (population approximately 1.8 million). In 1992, two groups of 25 healthy individuals were selected for 14 consecutive days of 24-hour personal monitoring, based on prior expectations of their activity patterns. The first group, composed of adult healthcare workers, was expected to spend most of the work day indoors or commuting. The second group, teenage camp counselors, was expected to spend more time outdoors. Time-activity data were collected to investigate the association between activity patterns and ozone exposures. In 1993, 15 adult farmworkers wore personal ozone samplers during their workday, which was spent entirely outdoors. Personal monitoring was conducted with a nitrite-coated filter passive ozone sampler described by Koutrakis and colleagues. Ozone collection rates were determined empirically by collocation of the passive samplers with continuous ozone analyzers at fixed sampling sites. Sampler performance was assessed by collecting several duplicate personal samples. Although ozone levels were low (< 35 ppb 24-hour average) during both summer sampling periods, the passive ozone samplers agreed well with collocated UV absorption ozone measurements. Based on replicate personal samples, we estimated that personal measurements differing by more than 35% were associated with true differences in exposure. Within the two groups with varying time activities, differences in ozone exposures were associated with the fraction of time spent outdoors. Similarly, differences in ozone exposures were observed between the three sampling populations, with higher exposures recorded in the group that spent more time outdoors.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗