Clinical decisionmaking.
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Decision Theory↗
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Diffusion in lattice Lorentz gases with a percolation threshold.
A mean-field approximation for the diffusion coefficient in lattice Lorentz gases with an arbitrary mixture of pointlike stochastic scatterers in the low-density limit is proposed. In this approximation, the diffusion coefficient is directly related to the first return probability of the moving particle in the corresponding Cayley tree through an effective ring operator. A renormalization scheme for the approximate determination of the first return probability is constructed. The predictions of this mean-field theory and those of the repeated ring approximation (RRA) are compared with computer simulation results for models in which a fraction x(B) of the scatterers are deterministic backscatterers, so that the diffusion coefficient vanishes beyond a certain percolation threshold x(c)(B). The approximation proposed in this paper is seen to be in good agreement with the simulation results, in contrast to the RRA, which already fails to give the correct percolation threshold.
Journal Article↗
Occam factors and model independent Bayesian learning of continuous distributions.
Learning of a smooth but nonparametric probability density can be regularized using methods of quantum field theory. We implement a field theoretic prior numerically, test its efficacy, and show that the data and the phase space factors arising from the integration over the model space determine the free parameter of the theory ("smoothness scale") self-consistently. This persists even for distributions that are atypical in the prior and is a step towards a model independent theory for learning continuous distributions. Finally, we point out that a wrong parametrization of a model family may sometimes be advantageous for small data sets.
Journal Article↗
Error-driven global transition in a competitive population on a network.
We show, both analytically and numerically, that erroneous data transmission generates a global transition within a competitive population playing the "Minority Game" on a network. This transition, which resembles a phase transition, is driven by a "temporal symmetry breaking" in the global outcome series. The phase boundary, which is a function of the network connectivity p and the error probability q, is described quantitatively by the crowd-anticrowd theory.
Adaptation, Physiological↗
Strong-coupling theory of two-level atoms in periodic fields
We present a new convergent strong-coupling expansion for two-level atoms in external periodic fields, free of secular terms. As a first application, we show that the coherent destruction of tunneling is a third-order effect. We also present an exact treatment of the high-frequency region, and compare it with the theory of averaging. The qualitative frequency spectrum of the transition probability amplitude contains an effective Rabi frequency.
Journal Article↗
Polymorphic light eruption--an immunopathological study of provoked lesions.
Polymorphic light eruption (PLE) lesions were induced in 26 patients after an average of 60 J total body UVA irradiation. Using the criteria of the French literature, that make a distinction between PLE and benign summer light eruption (BSLE), the group of 26 patients with PLE was divided into 12 patients with BSLE and 14 patients with PLE, on the basis of historical criteria. Biopsies were taken and compared immunohistochemically with biopsies from 15 unirradiated normal control subjects, in order to find evidence in support of the hypothesis that PLE involves a delayed-type hypersensitivity reaction. The provoked lesions showed: ICAM-1 expression on the keratinocytes of the basal and suprabasal cell layers in 18 of 25 patients, i.e. 72%; HLA-DR expression on the keratinocytes of the basal, squamous and granular cell layer in 13 of 25 patients, i.e. 52%; and OKM5 expression on the keratinocytes of the granular cell layer in 13 of 26 patients, i.e. 50% of the cases. The control samples showed no such antigen expression on the keratinocytes, except for two cases where weak and very localized ICAM-1 positivity was observed; one of these also had a slight localized positivity for HLA-DR and OKM5. The results of the phototesting procedures and the immunohistochemical investigations were similar in both BSLE and PLE. This suggests that they are the same condition, and the term BSLE should therefore probably be discarded. The results of our investigations support the theory of an immunological basis for PLE.
Adult↗
Ventricular ependyma of normal and hydrocephalic subjects: a scanning electronmicroscopic study.
Recent scanning electronmicroscopic studies of the ependymal surfaces of the lateral, third and fourth ventricles of a variety of animals have shown that most areas are covered by numerous cilia. In this paper, the density of the ciliary population in each of the ventricles is illustrated with material taken from human and rat brains. The authors' examination of Hy3 mice with hydrocephalus, and a number of other reports of examinations of animals with genetic and artificially induced hydrocephalus, have shown that the cilia are lost only from the ependymal surfaces covering those parts of the ventricular wall which are stretched and thinned by the raised intraventricular pressure. Thus the loss of the cilia is most probably the result of the hydrocephalus, and not its cause. Theories concerning the functions of the cilia are reviewed, and a new one accounting for why they are present in such large numbers is suggested. It is proposed that the cilia, together with the ventricular system and the cerebrospinal fluid, provide a cooling system for the brain.
Animals↗
Risk-taking and arousal regulation.
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Achievement↗
Volunteering as Red Queen mechanism for cooperation in public goods games.
The evolution of cooperation among nonrelated individuals is one of the fundamental problems in biology and social sciences. Reciprocal altruism fails to provide a solution if interactions are not repeated often enough or groups are too large. Punishment and reward can be very effective but require that defectors can be traced and identified. Here we present a simple but effective mechanism operating under full anonymity. Optional participation can foil exploiters and overcome the social dilemma. In voluntary public goods interactions, cooperators and defectors will coexist. We show that this result holds under very diverse assumptions on population structure and adaptation mechanisms, leading usually not to an equilibrium but to an unending cycle of adjustments (a Red Queen type of evolution). Thus, voluntary participation offers an escape hatch out of some social traps. Cooperation can subsist in sizable groups even if interactions are not repeated, defectors remain anonymous, players have no memory, and assortment is purely random.
Cooperative Behavior↗
Insertion-duplication mutagenesis in Streptococcus pneumoniae: targeting fragment length is a critical parameter in use as a random insertion tool.
To examine whether insertion-duplication mutagenesis with chimeric DNA as a transformation donor could be valuable as a gene knockout tool for genomic analysis in Streptococcus pneumoniae, we studied the transformation efficiency and targeting specificity of the process by using a nonreplicative vector with homologous targeting inserts of various sizes. Insertional recombination was very specific in targeting homologous sites. While the recombination rate did not depend on which site or region was targeted, it did depend strongly on the size of the targeting insert in the donor plasmid, in proportion to the fifth power of its length for inserts of 100 to 500 bp. The dependence of insertion-duplication events on the length of the targeting homology was quite different from that for linear allele replacement and places certain limits on the design of mutagenesis experiments. The number of independent pneumococcal targeting fragments of uniform size required to knock out any desired fraction of the genes in a model genome with a defined probability was calculated from these data by using a combinatorial theory with simplifying assumptions. The results show that efficient and thorough mutagenesis of a large part of the pneumococcal genome should be practical when using insertion-duplication mutagenesis.
Chimera↗
Human Phenome based on traditional Chinese medicine--a solution to congenital syndromology.
The occurrence of many congenital syndromes has long been an enigma. Clinically, the phenotype of any given genetic defect usually varies to some extent, whilst, pathogenetically, features within each syndrome are probably interconnected, albeit by largely unknown mechanisms. Through its unique theories such as the Jing-Mai (variously translated as the Channels, Vessels or Meridians), Zang-Fu (the Yin and Yang internal organs) and Wu-Xing (translated as the Five-Phase Correspondence or Five-Element theory), traditional Chinese medicine (TCM) seems to have comprehensively summarized the makeup of the human phenotypes. By combining the above TCM theories with modem medical knowledge, the intrinsic mechanisms between various aspects of the phenotypic makeup of the human individual, i.e. the Human Phenome, may be deduced. Analysis of congenital syndromes in light of the Human Phenome seems to suggest that various genetic defects may cause diseases in a similar fashion; i.e. primarily with structural abnormalities distributed along the four Jing-Mai connected with the Kidneys (midline defects) as well as "Marrow" aberrations (anomalies of hematology/immunology, endocrine, central nervous system and the bones). The derived Human Phenome may thereby enable a better understanding of such conditions and provide a model for the study of multigenic traits. On the other hand, blind spots of clinical observation and unknown aspects of human nature, e.g. circuits formed by the JingMai, symmetries of the Jing-Mai and Zang-Fu, and correspondences between body physiques, spiritual factors and the external world may also be deduced. The TCM-based Human Phenome may thereby offer a fresh view for genotype-phenotype correlations, insights into genedevelopment mechanisms, as well as potential directions for the development of new treatments.
Congenital Abnormalities↗
Decision maker, quantify thyself!
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Decision Theory↗
Efficient scheduling of cystoscopies in monitoring for recurrent bladder cancer.
Proper timing for repeated evaluations is difficult to assess. The authors analyzed scheduling of cystoscopy to monitor patients for detection of recurrent bladder cancer assuming that 1) minimizing tumor detection delay helps prevent cancer morbidities; 2) only limited numbers of cystoscopies are available; 3) prediction of recurrence or progression to invasive cancer is uncertain; 4) future tumors recur according to a Poisson process. Assumptions 3 and 4 permit estimation of each patient's recurrence rate. Thus, patients may be compared according to their relative risks of future tumors. With these assumptions, nonlinear optimization theory was used to calculate monitoring schedules for a model practice. Given 5.4 available visits per week per 100 patients, cystoscopy was recommended in 9-11 weeks for high-risk patients and in 30-40 weeks for low-risk patients, depending on stages, grades, and numbers of previous tumors. In contrast, standard cystoscopy was recommended in 13, 26, or 52 weeks, depending only on time elapsed since last recurrence. The calculated schedule implied an average detection delay for potentially invasive tumors of eight weeks, while standard practice led to detection delays of 11 weeks (38% worse). These results suggest that inclusion of each patient's tumor history in an optimization approach may improve follow-up care for patients who have superficial bladder cancers. This approach is being evaluated in a larger clinical setting.
Appointments and Schedules↗
A reconsideration of a thyroid-stimulating immunoglobulin as the cause of hyperthyroidism in Graves' disease.
Several assays for thyroid-stimulating immunoglobulins in the blood in patients with Graves' disease have been described recently; depending upon the method, different names have been used and distinct entities thus implied. Using an increase in cyclic AMP in the human thyroid slice after 2 h of incubation as an index of thyroid stimulation, we identified thyroid-stimulating activity in all of an unselected series of sera from 11 patients with hyperthyroidism of Graves' disease, but long-acting thyroid stimulator, by mouse bioassay, in only three. The theory is proposed that the thyroid-stimulating immunoglobulin is probably present in all such patients; it may be seen as a polyclonal antibody to a single human antigen that has a variable cross-reaction with a corresponding thyroid antigen in the mouse and in other species.
Animals↗
The role of therapeutic drug monitoring in improving the cost effectiveness of anticonvulsant therapy.
When monitoring of the plasma concentrations of anticonvulsant drugs first came into use 25 years ago, it appeared to have a major impact on improving the effectiveness and safety of anticonvulsant therapy. However, as time has passed, prescribers have absorbed many of the lessons to be learned from the monitoring, and now apply this knowledge without necessarily monitoring plasma anticonvulsant concentrations as frequently as in the past. Therefore, the effect of the drug concentration monitoring on the cost effectiveness of anticonvulsant therapy is probably not as significant now as it originally was. In theory, drug concentration monitoring is often unlikely to decrease the cost of contemporary anticonvulsant drug therapy, but it may enhance the efficacy of the therapy. Thus, monitoring may reveal unrecognised under- or overdosage, detect failure of compliance or drug-drug interactions, or indicate when there is little point in persisting with a particular anticonvulsant drug. Despite a good deal of anecdotal testimony, surprisingly little has been published demonstrating the benefits of anticonvulsant therapeutic drug monitoring in epileptic populations. However, one study did show better rates of seizure control rates in patients monitored in the first 6 months of their epileptic disorder; but not if the monitoring began later than this.(ABSTRACT TRUNCATED AT 250 WORDS)
Anticonvulsants↗
Bárány's theory is right, but incomplete. An experimental study in pigeons.
The horizontal semicircular canal in pigeons was thermally stimulated with a miniature Peltier-element device. Sound evoked electric responses from the vestibular organ were modulated by the caloric stimulus. Experiments were performed under minimal influence of gravity, (horizontal canals in horizontal plane), and with the pigeons head tilted forwards or backwards. On the basis of the results it was concluded that the influence of gravity can be described by Bárány's convection theory. Extra effects are, however, present and they are most probably partly of mechanical origin (fluid expansion) and partly due to a direct influence of temperature on the vestibular receptors. Further experiments are needed to investigate the origin of these extra effects in more detail.
Animals↗
In vitro effects of sulphasalazine, azodisal sodium, and their metabolites on Clostridium difficile and some other faecal bacteria.
The effects of sulphasalazine (SASP), azodisal sodium (ADS), and their metabolites were tested in vitro on aerobic and anaerobic faecal bacterial strains. Sulphapyridine (SP) had a mild to moderate effect on Escherichia coli and Streptococcus faecalis. SASP also had a growth-inhibitory effect on Strep. faecalis. The other substances had no effect on the aerobic strains. SASP, SP, 5-aminosalicylic acid, and, to a certain extent, N-acetyl-5-aminosalicylic acid exerted a growth-inhibitory effect on the anaerobic strains. Of special interest was the inhibitory effect on Clostridium difficile strains. In recent years the possibility that overgrowth of Cl. difficile could cause flare-ups of inflammatory bowel disease has been discussed. Some studies suggested that SASP treatment could predispose to Cl. difficile superinfection, whereas others found SASP more probable to exert a prophylactic effect. Our findings support the theory that SASP treatment reduces rather than promotes the risk of Cl. difficile superinfection.
Aminosalicylic Acids↗
Ethics of justice vs the ethics of care in moral decision making.
The question to be addressed in this paper is: How can the ethics of justice and the ethics of care be used complementary to each other in ethical decision making within the health care team? Various arguments are presented that justify the reasons that the ethics of justice and the ethics of care should be used complementary to each other for effective ethical decision making within the health care team. The objective is to explore and describe the compatibility of the ethics of justice and the ethics of care from two perspectives: firstly an analysis of the characteristics of the two ethical theories, and secondly the scientific-philosophical viewpoints of these theories. The two theories are incompatible when viewed from these perspectives. For a probable solution to this incompatibility arguments are presented from the perspectives of reflection and virtue-based ethics.
Decision Making↗