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PubMed2002

The orbital pulley system: a revolution in concepts of orbital anatomy.

Magnetic resonance imaging (MRI) now enables precise visualization of the mechanical state of the living human orbit. Resulting insights have motivated histological re-examination of human and simian orbits, providing abundant consistent evidence for the active pulley hypothesis, a re-formulation of ocular motor physiology. Each extraocular muscle (EOM) consists of a global layer (GL) contiguous with the tendon and inserting on the eyeball, and a similar-sized orbital layer (OL) inserting on a connective tissue ring forming the EOM pulley. The pulley controls the EOM path and serves as the EOM's functional origin. Activity of the OL positions the pulley along each rectus EOM to assure that its pulling direction shifts by half the change in ocular orientation, the half-angle behavior characteristic of a linear ocular motor plant. Half-angle behavior is equivalent to Listing's law of ocular torsion, and makes 3-D ocular rotations effectively commutative. Pulleys are configured to maintain oblique EOM paths orthogonal to half-angle behavior, and violate Listing's law during the vestibulo-ocular reflex. Rectus pulley positions shift during convergence, facilitating stereopsis. Innervations, fiber types, and metabolism of the OL and GL differ, consistent with the elastic loading of the former, and viscous loading of the latter. Disorders of the location and stability of rectus pulleys are associated with predictable patterns of incomitant strabismus that may mimic cranial nerve palsies. Surgical interventions improve defective pulley function. Understanding of ocular motor control requires characterization of the behavior of the EOM pulleys as well as knowledge of angular eye orientation.

Adult↗
PubMed2003

Environmental conditions unexpectedly affect the long-term extent of cell death following an hypoxic episode.

Previously we reported delayed cell death, defined by clear-cut cell loss 60 days after a nitrite-induced hypoxic episode. The loss of cells was not apparent two weeks after the treatment, although some changes in cellular appearance were observed at that time. A similar delayed loss of neurons in the hippocampus after hypoxia induced by blood vessel occlusion has also been found. In addition, we reported that the amount of methemoglobinemia induced by the sodium nitrite can be reduced by the stress produced by handling and the injection of saline 2 or 24 h before the nitrite administration. The degree of methemoglobin formed is directly related to cell death in certain areas of the brain, including regions within the hippocampus. Considering the many effects that can be produced by chronic and acute stress of several kinds and the length of time during which these effects manifest themselves, we undertook to determine the histologic effects of the stresses of transport on the neuroanatomic effects of sodium nitrite administration 60 days post administration. Comparisons were made of the effects of two methods of transport from the laboratory in which the animals (male CD-1 mice) were injected with the sodium nitrite or saline (Tufts Medical School) to the laboratory in which the histologic evaluations were made (Binghamton University). The animals began their travel several hours after the injections. One transport method was by commuter airline and the other was by automobile. All animals had the same transport from the supplier to the Boston location (truck). Thus, the stress of experimental interest occurred after the nitrite administration. Upon arrival at Binghamton University, the animals were housed at the University in their own colony room for 60 days before sacrifice. After sacrifice, sections from their brains were subjected to a number of histologic staining procedures, including PTAH, the Bielschowsky silver method, GFAP, and the standard Nissl procedure. Although special attention was paid to hippocampal areas, changes in cells in the habenulae and the linings of ventricular areas were also prominent. Surprisingly, the nitrite treatment before transport to Binghamton offered partial protection against the very substantial and lasting effects of the injections, transport, and handling found in the control animals. Differential effects caused by the two methods of transport were also noted.

Animals↗
PubMed1986

Wolff's law of trabecular architecture at remodeling equilibrium.

An elastic constitutive relation for cancellous bone tissue is developed. This relationship involves the stress tensor T, the strain tensor E and the fabric tensor H for cancellous bone. The fabric tensor is a symmetric second rank tensor that is a quantitative stereological measure of the microstructural arrangement of trabeculae and pores in the cancellous bone tissue. The constitutive relation obtained is part of an algebraic formulation of Wolff's law of trabecular architecture in remodeling equilibrium. In particular, with the general constitutive relationship between T, H and E, the statement of Wolff's law at remodeling equilibrium is simply the requirement of the commutativity of the matrix multiplication of the stress tensor and the fabric tensor at remodeling equilibrium, T*H* = H*T*. The asterisk on the stress and fabric tensor indicates their values in remodeling equilibrium. It is shown that the constitutive relation also requires that E*H* = H*E*. Thus, the principal axes of the stress, strain and fabric tensors all coincide at remodeling equilibrium.

Bone and Bones↗
PubMed1998

New classes of helical weighting algorithms with applications to fast CT reconstruction.

The focus of this paper is on CT helical weighting algorithms using one source rotation, or 2 pi, worth of projection data. Currently known 2 pi helical weighting algorithms include a fan-angle dependency, and do not lend themselves to fast reconstruction, for two reasons. First, it can be shown that the weight distributions present a line of discontinuity across the sinogram (projection space), which defines two separate sinogram regions. Second, the expressions for the weighting functions differ for those two regions. Accordingly, reconstruction of P different image planes (all using a given projection) requires P weightings and filterings of that projection. In this paper, it is shown that, by first generalizing the concept of the interpolation/extrapolation function used in the weighting, to the concept of distance function, and second by selecting particular classes of such distance functions, the discontinuity across the sinogram can be eliminated. By imposing specific sufficient conditions on such distance functions, single analytical expressions across the entire 2 pi sinogram are obtained. Decomposition of these particular "single" distance functions leads to two-filtering reconstruction algorithms, for which a given projection needs to be filtered only two times for an arbitrary number P of reconstruction planes. Finally, another generalization of the concept of helical weighting leads to one-filtering weight functions that depend only on the sum of the projection--and fan angles. Accordingly, after rebinning the fan-beam projections to parallel projections, the corresponding 2 pi helical weighting algorithms do not include a dependency over the ray parameter. Equivalently, for these algorithms, weighting commutes with filtering, and reconstruction of an arbitrary number P of image planes requires only one filtering per projection. These algorithms are shown to be consistent with the hypothesis of a linear z variation of the projections.

Algorithms↗
PubMed2000

A principle of least complexity for musical scales.

The following properties of equally tempered scales are demonstrated in this Letter: For N semitones and M notes, each distinct scale (interval) structure can be represented by an associated multiplet of N scales. These scales allow themselves to be labeled by a set of integers ¿c¿. Each label c is the difference between the number of sharps and flats in a given scale. The equivalence classes [c] modulo N form a commutative ring with unity. When the ratio N/M cannot be simplified further, then each member of a given multiplet will have a unique label (modulo N), different from the other members of the same multiplet. Because this labeling depends not on the interval structure of the multiplet but only on N and M, different multiplets with the same N and M values will have members carrying the same respective labels. Each equally tempered scale (interval) structure possesses a property which will be referred to as complexity. This Letter proposes a quantitative measure for complexity which distinguishes between different scale (interval) structures. For the particular case where N= 12 and M=7, out of 462 possible different equally tempered scale structures, those with minimum complexity are the major scale and the modes, which suggests a minimum principle in music based on equally tempered scales. This simplicity of structure allows the practical use of key signatures in music.

Models, Theoretical↗
PubMed2003

Focusing on the big picture.

As a postdoc in cognitive neuroscience who's also a neurology fellow, Adam Gazzaley is a meld of basic science expertise and clinical experience: He studies brain aging in people by using functional magnetic resonance imaging at the University of California (UC), Berkeley, and he also sees patients at UC San Francisco's Memory and Aging Center. The 34-year-old native New Yorker dives with equal fervor into scientific research and nature photography, two lenses for viewing a single world of discovery. Growing up in Queens, Gazzaley knew from age 7 that he wanted to become a scientist, and as a teenager, he commuted long hours to attend the Bronx High School of Science. He earned an M.D.-Ph.D. from the Mount Sinai School of Medicine in New York City. Gazzaley's hobby as a shutterbug periodically takes him on backpacking trips to document the beauty of the great outdoors. He sells fine-art prints of his photographs to individuals, hospitals, and clinics through his company, Wanderings Inc.

Brain↗
PubMed2006

Synchrony, waves, and spatial hierarchies in the spread of influenza.

Quantifying long-range dissemination of infectious diseases is a key issue in their dynamics and control. Here, we use influenza-related mortality data to analyze the between-state progression of interpandemic influenza in the United States over the past 30 years. Outbreaks show hierarchical spatial spread evidenced by higher pairwise synchrony between more populous states. Seasons with higher influenza mortality are associated with higher disease transmission and more rapid spread than are mild ones. The regional spread of infection correlates more closely with rates of movement of people to and from their workplaces (workflows) than with geographical distance. Workflows are described in turn by a gravity model, with a rapid decay of commuting up to around 100 km and a long tail of rare longer range flow. A simple epidemiological model, based on the gravity formulation, captures the observed increase of influenza spatial synchrony with transmissibility; high transmission allows influenza to spread rapidly beyond local spatial constraints.

Adult↗
PubMed2006

Children as partners with adults in their medical care.

AIMS: To investigate the seldom published views of children with type 1 diabetes about their condition and ways in which they share in managing their medical and health care with adults. METHODS: Semi-structured, tape recorded interviews, during 2003, with a purposive sample of 24 children aged 3-12 years who have type I diabetes and who attend two inner London hospitals and one hospital in a commuter town. RESULTS: The children reported high levels of understanding, knowledge, and skill gained from their experience of living with diabetes and constantly having to take account of the condition and their paediatrician's guidance. Their key goals were to be "normal" and "just get on with their lives". DISCUSSION: The interviews showed that children's experiences of diabetes tended to enable them to make informed, "wise" decisions in their own best interests, even at a young age. They achieved a complicated balance between the sometimes competing goals of social health "being normal" and physiological health in controlling glycaemia. Their competence supports approaches in children's rights and in policy makers' aims that people with diabetes--including children--gain more knowledge, skills, and responsibility for their own care in partnership with healthcare professionals. Consent is usually considered in relation to surgery; however the children showed how they constantly dealt with decisions about consent or refusal, compliance with, or resistance to their prescribed treatment. Their health depends on their informed commitment to medical guidance; more research is needed about the daily realities of children's committed and responsible co-management of their chronic illness.

Adult↗
PubMed1993

Comparison of attendance and emergency admission patterns at accident and emergency departments in and out of London.

OBJECTIVE: To compare the sociodemographic characteristics, diagnoses, and mode of referral of people and emergency admissions between an accident and emergency department in inner London and one in a town outside London. DESIGN: Standardised questionnaire completed prospectively over two weeks by field-workers in each accident and emergency department. SETTING: Accident and emergency departments in an inner London teaching hospital and an associated teaching hospital outside London. SUBJECTS: 3039 adults newly attending the departments, 1476 in inner London and 1563 outside London. MAIN OUTCOME MEASURES: Sociodemographic characteristics, diagnosis, mode of referral, and whether the patient was admitted. RESULTS: General practitioner referrals accounted for similar proportions of the adult attendances (12% in inner London, 15% outside London). People attending at the inner London department were more likely to be tourists or long distance commuters (12% (179/1476) v 6% (95/1563)), single (43% (643) v 32% (505)), to live alone (24% (360) v 14% (225)), to have moved recently (13% (194) v 7% (107)), or to be homeless (3.3% (48) v 0.6% (10)). Broad clinical groupings of patients were similar in both departments. 291 people were admitted in inner London and 284 outside London. The proportions admitted from each sociodemographic group were similar in the two hospitals. CONCLUSION: Differences in sociodemographic characteristics were more important than general practice referral patterns in determining the differences in people attending at accident and emergency departments inside and outside London. Many of these characteristics are likely to be found in other inner city populations. A strategy to improve acute care in inner London should take account of the needs of these sociodemographically different groups.

Adult↗
PubMed2001

Use of protective equipment by in-line skaters: an observational study.

OBJECTIVE: To determine the extent of protective equipment use (that is, helmets, wrist guards, elbow pads, knee pads) in a representative sample of in-line skaters. SETTING: Fifteen municipalities throughout the province of British Columbia. METHOD: A province-wide observational survey was conducted in the summer of 1999. Skaters were observed at four types of sites (commuter, recreational, neighbourhood, general community) in 15 municipalities to provide a representative sample of in-line skaters. RESULTS: The observed use of protective equipment by the 877 in-line skaters was relatively low: wrist guards 25%, helmets 13%, elbow pads 14%, and knee pads 10%. CONCLUSION: Despite the availability of relatively inexpensive protective equipment, few in-line skaters take advantage of the opportunity to protect themselves from injury. Policies and programs that serve to increase the use of protective equipment by in-line skaters are needed to help reduce the frequency of skating related injuries.

Adolescent↗
PubMed2003

Human organs from prisoners: kidneys for life.

A proposal to allow prisoners to save their lives or to be eligible for commutation of sentence by donating kidneys for transplantation has been a subject of controversy in the Philippines. Notwithstanding the vulnerabilities associated with imprisonment, there are good reasons for allowing organ donations by prisoners. Under certain conditions, such donations can be very beneficial not only to the recipients but to the prisoners themselves. While protection needs to be given to avoid coercion and exploitation, overprotection has to be avoided. The prohibition on the involvement of prisoners in organ transplantation constitutes unjustified overprotection. Under certain conditions, prisoners can make genuinely independent decisions. When it can be reasonably ascertained that they are able to decide freely, society should recognise an obligation to help them implement their decisions, such as when they intend to donate an organ as a way of asserting their religious faith and performing a sacrifice in atonement for their sins.

Attitude to Health↗
PubMed2005

The London Underground: dust and hazards to health.

AIMS: To assess hazards associated with exposure to dust in the London Underground railway and to provide an informed opinion on the risks to workers and the travelling public of exposure to tunnel dust. METHODS: Concentrations of dust, as mass (PM2.5) and particle number, were measured at different underground stations and in train cabs; its size and composition were analysed; likely maximal exposures of staff and passengers were estimated; and in vitro toxicological testing of sample dusts in comparison with other dusts was performed. RESULTS: Concentrations on station platforms were 270-480 microg/m3 PM2.5 and 14,000-29,000 particles/cm3. Cab concentrations over a shift averaged 130-200 microg/m3 and 17,000-23,000 particles/cm3. The dust comprised by mass approximately 67% iron oxide, 1-2% quartz, and traces of other metals, the residue being volatile matter. The finest particles are drawn underground from the surface while the coarser dust is generated by interaction of brakes, wheels, and rails. Taking account of durations of exposure, drivers and station staff would have maximum exposures of about 200 microg/m3 over eight hours; the occupational exposure standard for welding fume, as iron oxide, is 5 mg/m3 over an eight hour shift. Toxicology showed the dust to have cytotoxic and inflammatory potential at high doses, consistent with its composition largely of iron oxide. DISCUSSION: It is unjustifiable to compare PM2.5 exposure underground with that on the surface, since the adverse effects of iron oxide and combustion generated particles differ. Concentrations of ultrafine particles are lower and of coarser (PM2.5) particles higher underground than on the surface. The concentrations underground are well below allowable workplace concentrations for iron oxide and unlikely to represent a significant cumulative risk to the health of workers or commuters.

Air Pollutants↗
PubMed2005

The impact of overtime and long work hours on occupational injuries and illnesses: new evidence from the United States.

AIMS: To analyse the impact of overtime and extended working hours on the risk of occupational injuries and illnesses among a nationally representative sample of working adults from the United States. METHODS: Responses from 10,793 Americans participating in the National Longitudinal Survey of Youth (NLSY) were used to evaluate workers' job histories, work schedules, and occurrence of occupational injury and illness between 1987 and 2000. A total of 110,236 job records were analysed, encompassing 89,729 person-years of accumulated working time. Aggregated incidence rates in each of five exposure categories were calculated for each NLSY survey period. Multivariate analytical techniques were used to estimate the relative risk of long working hours per day, extended hours per week, long commute times, and overtime schedules on reporting a work related injury or illness, after adjusting for age, gender, occupation, industry, and region. RESULTS: After adjusting for those factors, working in jobs with overtime schedules was associated with a 61% higher injury hazard rate compared to jobs without overtime. Working at least 12 hours per day was associated with a 37% increased hazard rate and working at least 60 hours per week was associated with a 23% increased hazard rate. A strong dose-response effect was observed, with the injury rate (per 100 accumulated worker-years in a particular schedule) increasing in correspondence to the number of hours per day (or per week) in the workers' customary schedule. CONCLUSIONS: Results suggest that job schedules with long working hours are not more risky merely because they are concentrated in inherently hazardous industries or occupations, or because people working long hours spend more total time "at risk" for a work injury. Strategies to prevent work injuries should consider changes in scheduling practices, job redesign, and health protection programmes for people working in jobs involving overtime and extended hours.

Accidents, Occupational↗
PubMed2003

Coverage of work related fatalities in Australia by compensation and occupational health and safety agencies.

AIMS: To determine the levels of coverage of work related traumatic deaths by official occupational health and safety (OHS) and compensation agencies in Australia, to allow better understanding and interpretation of officially available statistics. METHODS: The analysis was part of a much larger study of all work related fatalities that occurred in Australia during the four year period 1989 to 1992 inclusive and which was based on information from coroners' files. For the current study, State, Territory, and Commonwealth OHS and compensation agencies were asked to supply unit record information for all deaths identified by the jurisdictions as being due to non-suicide traumatic causes and which were identified by them as being work related, using whatever definitions the agencies were using at the relevant time. This information was matched to cases identified during the main study. RESULTS: The percentage of working deaths not covered by any agency was 34%. Only 35% of working deaths were covered by an OHS agency, while 57% were covered by a compensation agency. The OHS agencies had minimal coverage of work related deaths that occurred on the road (to workers (8%) or commuters (3%)), whereas the compensation system covered these deaths better than those of workers in incidents that occurred in a workplace (65% versus 53%). There was virtually no coverage of bystanders (less than 8%) by either type of agency. There was marked variation in the level of coverage depending on the industry, occupation, and employment status of the workers, and the type of injury event involved in the incident. CONCLUSIONS: When using data from official sources, the significant limitations in coverage identified in this paper need to be taken into account. Future surveillance, arising from a computerised National Coroners Information System, should result in improved coverage of work related traumatic deaths in Australia.

Accidents, Occupational↗
PubMed1989

STD and contraception in adolescents.

The prevalence of sexually transmitted diseases (STDs) in adolescents is poorly documented, as published studies consider single diseases or subgroups of adolescents. To obtain a broader view we examined STDs in unselected adolescent boys and girls at two contrasting genitourinary medicine (GUM) clinics, a large one at St Thomas's Hospital in inner London, which serves commuters and an inner city population, the other a smaller one at Swansea in south Wales, which serves a mixed urban and rural population. Contraception was also assessed in the girls. The STDs in adolescents were compared with the total diagnoses in patients of all ages attending the two GUM clinics, and with total diagnoses in all patients attending GUM clinics in England and Wales. The most striking finding was that all adolescents had at least one infection, whereas 18% of diagnoses in patients of all ages were of no infection. This contrasts with results of previous studies of selected groups, which suggested that the prevalence of STDs is similar in adults and adolescents. The percentages of infections, other than herpes at both clinics and trichomoniasis at Swansea, were higher in adolescents than in patients of all ages. High incidences of pelvic inflammatory disease in London and genital warts at Swansea suggest future problems. Only 66% of adolescent girls practised contraception, and only 8% stated that condoms were used. All people caring for adolescents should consider whether they are sexually active and, if they are, whether they need contraceptive advice or referral to a GUM clinic.

Adolescent↗
PubMedDate not supplied

Models of Hopfield-type quaternion neural networks and their energy functions.

Recently models of neural networks that can directly deal with complex numbers, complex-valued neural networks, have been proposed and several studies on their abilities of information processing have been done. Furthermore models of neural networks that can deal with quaternion numbers, which is the extension of complex numbers, have also been proposed. However they are all multilayer quaternion neural networks. This paper proposes models of fully connected recurrent quaternion neural networks, Hopfield-type quaternion neural networks. Since quaternion numbers are non-commutative on multiplication, some different models can be considered. We investigate dynamics of these proposed models from the point of view of the existence of an energy function and derive their conditions for existence.

Algorithms↗
PubMed1981

Studies on the phenomenon of latent propagated sensation along the channels. I. The discovery of a latent PSC and a preliminary study of its skin electrical conductance.

By combining electrical impulse stimuli with mechanical ones, we are able to trace out a new line of feeling, coincident with the classical channel course. Impulse stimulation was carried out at the Jing point of the Large Intestine or Stomach channel, namely Shangyan or Lidui. With a small rubber nipple, light taps were applied on the skin along the lines perpendicular to the channel and crossing over the acupuncture points; a specific propagational numb feeling at the points of the channel could be found. By linking up these points of specific feeling, an imaginary line which is exactly the classical Large Intestine or Stomach channel can be traced out. This line is called the "latent propagational sensation line along the channels" because, unless through tapping, no prominent sensation of propagation could be felt. Employing an impulsive electrical generator and an all-wave commutating circuit linked to a micro-ammeter, the skin conductance was measured over the latent PSC of the Large Intestine channel lying between the wrist and 5 cm above the elbow joint. Results were compared to those locations of 1 cm apart from the channel course, i.e. the control sites devoid of acupuncture points or channels. At most acupuncture points or any site of the channel course on all of the 10 subjects under examination, there was greater electrical conductance maxima than there was at control sites. This fact indicates that not only the acupuncture points, but the entire course of latent PSC are also of higher electrical conductance.

Acupuncture Therapy↗
PubMed1996

High plasma cholesterol, but low triglycerides and plaque-free arteries, in Mexican free-tailed bats.

Female mammals typically become hyperphagic from mid- to late pregnancy and during lactation. Mexican free-tailed bats, Tadarida brasiliensis mexicana, double their nightly food intake from late pregnancy to peak lactation and consume an insect diet that is exceptionally high in fat. During late pregnancy and throughout lactation, fasting plasma levels of cholesterol in this insectivorous bat are high (215 +/- 8 mg/dl) and are nearly 10-fold higher than in three species of Old World frugivorous bats. Fasting triglycerides were unexpectedly low in T. brasiliensis (25 +/- 2 mg/dl), despite evidence of high fat intake during nightly feeding bouts (postprandial cholesterol and triglycerides, 268 +/- 18 and 122 +/- 20 mg/dl, respectively). High-density lipoprotein (HDL) cholesterol levels were extraordinarily high (124 +/- 5 mg/dl) and unaffected by feeding. Low-density lipoprotein cholesterol levels were correspondingly low (86 +/- 7 mg/dl). This unusual plasma lipid profile was not associated with coronary or aortic atherosclerosis, nor was there evidence of hyperglycemia or hyperinsulinemia. A high-fat diet and high levels of cholesterol in T. brasiliensis are not correlated with cardiovascular disease or (possibly) insulin resistance. Among several possible factors that might account for these observations, nightly bouts of powered flight (commuting and foraging for food) may contribute to elevated HDL cholesterol, which may protect this species from developing atherosclerosis.

Animals↗