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PubMed1983

Carcinoembryonic antigen in retinoblastoma. An immunohistochemical study.

Pathological amounts of carcinoembryonic antigen (CEA) have earlier been reported in the plasma of patients with retinoblastoma, and it has been suggested that CEA determinations be used in the follow-up of treatment of these patients. In the present study, 47 retinoblastoma specimens from the years 1962-1982 were examined. These specimens represented different clinical and pathological tumour types. Colon adenocarcinomata positive for CEA were used as controls. The laboratory method was a highly sensitive immunohistochemical peroxidase-staining procedure. By this method, CEA was not found in any of the retinoblastomata examined. It is probable that retinoblastoma does not produce CEA, but in theory it may indirectly increase the CEA titre or, on the other hand, be fully independent of CEA. Only after this relationship has been thoroughly clarified can determinations of plasma CEA in patients with retinoblastoma be used in clinical work.

Adult↗
PubMed1989

Tutorial on large deviations for the binomial distribution.

We present, in an easy to use form, the large deviation theory of the binomial distribution: how to approximate the probability of k or more successes in n independent trials, each with success probability p, when the specified fraction of successes, a identical to k/n, satisfies 0 less than p less than a less than 1.

Amino Acid Sequence↗
PubMed2004

Clinical epidemiology of testicular germ cell tumors.

Clinical epidemiology is sometimes called the basic science of clinical medicine. In terms of the pathogenesis of testicular germ cell tumors (GCTs), clinical epidemiology analyzes suspected risk factors. The present review highlights the risk factors established so far and briefly summarizes those factors currently under investigation. In analogy to the methods of evidence based medicine, this review attributes levels of evidence to each of the putative risk factors. Level I represents highest quality of evidence while level V denotes the lowest level. So far, undescended testis (UDT), contralateral testicular GCT and familial testis cancer are established risk factors attaining high levels of evidence (levels I-III a). In a meta-analysis of 21 studies exploring the association of UDT with GCT risk, an over-all relative risk (RR) of 4.8 (95% confidence interval 4.0-5.7) was found. Contralateral testicular GCT involves a roughly 25-fold increased RR of GCT, while familial testis cancer constitutes a RR of 3-10. Infertility, testicular atrophy, and twin-ship represent risk factors with lesser levels of evidence (level III a). There is also some evidence for HIV infection being a predisposing factor for GCT (level IV a). Scrotal trauma is probably not associated with GCT risk. The estrogen excess theory implies high estrogen levels during the first trimester of pregnancy. As a consequence, primordial germ cells lose track of the normal developmental line and transform into premalignant cells that later become testicular intraepithelial neoplasia (TIN), the precursor of full-blown testicular GCT. Surrogate parameters for high gestational estrogen levels are investigated in case control studies. Such factors are maternal age >30 years, first-born, low birth weight, maternal breast cancer, high sex-ratio of siblings. So far, the sum of evidence is promising but still conflicting (especially for level III b). Another novel theory is the childhood nutrition hypothesis. This concept postulates a modulating or "catalyzing" effect by high dietary intake during childhood on the pathogenesis of testicular GCT. A surrogate parameter of early childhood nutrition is adult height. So far, 12 controlled studies have looked to the possible association of attained height and GCT risk of which six demonstrated a significant association. Thus, the sum of evidence corresponds to level III b. This concept is appealing because it would explain several hitherto unexplained epidemiological features of GCT.

Animals↗
PubMed1979

Bifurcation in non-negotiable games: a paradigm for self-organisation in cognitive systems.

The interaction between two self-organising systems, each possessing two hierarchical levels, is dealt with. The communication process is pursued as a bidirectional information transfer. The criterion for the selection of the intrasystem control algorithm(s) is based on the maximisation of the 'Joint Figure of Merit' related to the long-term average of an appropriately weighted sum of conflicting terms: Probabilities of homeostases versus adequate matching with the partner.

Behavior↗
PubMed2005

Learning and decision making in monkeys during a rock-paper-scissors game.

Game theory provides a solution to the problem of finding a set of optimal decision-making strategies in a group. However, people seldom play such optimal strategies and adjust their strategies based on their experience. Accordingly, many theories postulate a set of variables related to the probabilities of choosing various strategies and describe how such variables are dynamically updated. In reinforcement learning, these value functions are updated based on the outcome of the player's choice, whereas belief learning allows the value functions of all available choices to be updated according to the choices of other players. We investigated the nature of learning process in monkeys playing a competitive game with ternary choices, using a rock-paper-scissors game. During the baseline condition in which the computer selected its targets randomly, each animal displayed biases towards some targets. When the computer exploited the pattern of animal's choice sequence but not its reward history, the animal's choice was still systematically biased by the previous choice of the computer. This bias was reduced when the computer exploited both the choice and reward histories of the animal. Compared to simple models of reinforcement learning or belief learning, these adaptive processes were better described by a model that incorporated the features of both models. These results suggest that stochastic decision-making strategies in primates during social interactions might be adjusted according to both actual and hypothetical payoffs.

Algorithms↗
PubMed2005

Early and late processes in syllogistic reasoning: evidence from eye-movements.

An eye-movement monitoring experiment was carried out to examine the effects of the difficulty of the problem (simple versus complex problems) and the type of figure (figure 1 or figure 4) on the time course of processing categorical syllogisms. The results showed that the course of influence for these two factors is different. We found early processing effects for the figure but not for the difficulty of the syllogism and later processing effects for both the figure and the difficulty. These results lend support to the Model Theory (Johnson-Laird, P. N., Byrne, R. M. J. (1991). Deduction. Hillsdale, New Jersey: LEA.) as opposed to other theories of reasoning (Chater, N., Oaksford, M. (1999). The probability heuristics model of syllogistic reasoning. Cognitive Psychology, 38, 191-258; Rips, L. J. (1994). The psychology of proof. Cambridge, MA: MIT Press; Rips, L. J. (1994). The psychology of proof. Cambridge, MA: MIT Press).

Cognition↗
PubMed2003

Computational design and characterization of a monomeric helical dinuclear metalloprotein.

The de novo design of di-iron proteins is an important step towards understanding the diversity of function among this complex family of metalloenzymes. Previous designs of due ferro (DF) proteins have resulted in tetrameric and dimeric four-helix bundles having crystallographically well-defined structures and active-site geometries. Here, the design and characterization of DFsc, a 114 residue monomeric four-helix bundle, is presented. The backbone was modeled using previous oligomeric structures and appropriate inter-helical turns. The identities of 26 residues were predetermined, including the primary and secondary ligands in the active site, residues involved in active site accessibility, and the gamma beta gamma beta turn between helices 2 and 3. The remaining 88 amino acid residues were determined using statistical computer aided design, which is based upon a recent statistical theory of protein sequences. Rather than sampling sequences, the theory directly provides the site-specific amino acid probabilities, which are then used to guide sequence design. The resulting sequence (DFsc) expresses well in Escherichia coli and is highly soluble. Sedimentation studies confirm that the protein is monomeric in solution. Circular dichroism spectra are consistent with the helical content of the target structure. The protein is structured in both the apo and the holo forms, with the metal-bound form exhibiting increased stability. DFsc stoichiometrically binds a variety of divalent metal ions, including Zn(II), Co(II), Fe(II), and Mn(II), with micromolar affinities. 15N HSQC NMR spectra of both the apo and Zn(II) proteins reveal excellent dispersion with evidence of a significant structural change upon metal binding. DFsc is then a realization of complete de novo design, where backbone structure, activity, and sequence are specified in the design process.

Amino Acid Sequence↗
PubMed1999

Pubertal changes in hormone levels and depression in girls.

BACKGROUND: Throughout their reproductive years, women suffer from a higher prevalence of depression than men. Before puberty, however, this is not the case. In an earlier study, we found that reaching Tanner Stage III of puberty was associated with increased levels of depression in girls. This paper examines whether the morphological changes associated with puberty (as measured by Tanner stage) or the hormonal changes underlying them are more strongly associated with increased rates of depression in adolescent girls. METHODS: Data from three annual waves of interviews with 9 to 15-year-olds from the Great Smoky Mountains study were analysed. RESULTS: Models including the effects of testosterone and oestradiol eliminated the apparent effect of Tanner stage. The effect of testosterone was non-linear. FSH and LH had no effects on the probability of being depressed. CONCLUSIONS: These findings argue against theories that explain the emergence of the female excess of depression in adulthood in terms of changes in body morphology and their resultant psychosocial effects on social interactions and self-perception. They suggest that causal explanations of the increase in depression in females need to focus on factors associated with changes in androgen and oestrogen levels rather than the morphological changes of puberty.

Adolescent↗
PubMed2002

Hygroscopicity of aerosol particles at low temperatures. 2. Theoretical and experimental hygroscopic properties of laboratory generated aerosols.

A Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) system has been used to measure hygroscopic growth curves and deliquescence relative humidities (DRH) of laboratory generated (NH4)2SO4, NaCl, and NaNO3 particles at temperatures T= 20 degrees C and -10 degrees C. Good agreement (better than 3.5%) between measured growth curves and Köhler theory was found using empirical temperature and concentration dependent values for water activity, solution density, and surface tension. The measured growth curves only experience a small temperature dependence in the observed temperature range. Therefore, to a first approximation, it is possible to neglect the temperature dependence of the water activity for theoretical calculations in the temperature range -10 degrees C < T < 25 degrees C. The small differences between experiment and theory, which were predominantly observed for NaCl particles, are probably caused by a small amount of water adsorbed on the "dry" crystals. It was also observed that these particles experience a significant restructuring at relative humidity RH < DRH, which was also taken into account for a comparison with theoretical curves. If salt particles are used for instrument calibration, precautions regarding the dry particle diameter have to be taken.

Adsorption↗
PubMed2005

Two-dimensional supercritical behavior of an ethanol monolayer: a molecular dynamics study.

The two-dimensional (2D) supercritical behavior of an ethanol monolayer formed at the vapor/liquid interface of an ethanol solution has been investigated by a molecular dynamics (MD) calculations with a combination of the OPLS-UA and SPC/E potential models. A 100 A thick slab of ethanol solution was placed at the volume center of the rectangular unit cell by 10 A thick nonabsorbate water surfaces. With such an initial configuration, five independent 15 ns NVT constant MD calculations were carried out under 298.15 K, in which the initial ethanol mole fraction of the bulk solution layer was set to 0.010, 0.022, 0.045, 0.10, and 0.20, respectively. The 2D radial distribution function (rdf) of an adsorbed ethanol molecule showed that the ethanol monolayer could be regarded as a 2D fluid where the adsorbed ethanol molecule had an effective 2D diameter of 4.65 A. On the basis of the 2D rdf result, 2D cluster analysis was carried out from the perspective of the percolation theory. It is confirmed that the critical area occupation probability density, the critical exponents, and the fractal dimension of both nonpercolating and percolating clusters satisfied their nature of universality. Therefore, we concluded that an ethanol monolayer formed at the vapor/liquid interface of ethanol solution behaves as a 2D supercritical fluid at 298.15 K.

Journal Article↗
PubMed1997

Development of a statistical model for the formation of poly [acryloyl hydroxyethyl starch] microspheres.

PURPOSE: To develop a mathematical model for predicting the molecular weight between crosslinks, Mc, of poly[Acryloyl Hydroxyethyl Starch] (Ac-HES) microspheres system and to identify and evaluate the key microsphere preparation parameters which affect the Mc of the formed microsphere structure based on the developed model. METHODS: Link probability generating functions (LPGFs) based on the classical branching theory were used to derive a model for the calculation of Mc for the Ac-HES system. Based on the developed model, simulation was made to study the effects of the microsphere preparation variables on Mc of the formed microspheres. The process variables were the degree of derivatization (DD) of the Ac-HES, the molar ratio (MR) of the Ac-HES to acrylamide monomer, the fractional conversion of the unsaturation (alpha), the initiator efficiency (f), the molar concentration of initiator (I), the fraction of intramolecular cyclization (c), and the total weight of the reactable monomer and polymer (s). RESULTS: A model to describe the crosslinking reaction of Ac-HES system and predict Mc was developed. Simulation based on the model showed that Mc decreased as alpha increased and reached a limiting value before total conversion. At constant alpha, Mc initially decreased with MR to a minimum and then increased with MR; while Mc decreased monotonically with DD. I and c affected Mc only at very low alpha and changes in s and f had no effect on Mc. CONCLUSIONS: Simulation based on the model suggested that the most important microsphere preparation parameters influencing Mc of the Ac-HES system are the number of functional groups on the Ac-HES (DD) and the stoichiometry (MR) of the crosslinking reaction.

Acrylic Resins↗
PubMed1990

Judgments of proportions.

This study investigated the processes that underlie estimates of relative frequency. Ss performed 4 tasks using the same stimuli (squares containing black and white dots); they judged "percentages" of white dots, "percentages" of black dots, "ratios" of black dots to white dots, and "differences" between the number of black and white dots. Results were consistent with the theory that Ss used the instructed operations with the same scale values in all tasks. Despite the use of the correct operation, Ss consistently overestimated small proportions and underestimated large proportions. Variations in the distributions of actual proportions affected the extent to which Ss overestimated small proportions and underestimated large proportions in the direction predicted by range-frequency theory. Results suggest that proportion judgments, and by analogy probability judgments, should not be taken at face value.

Adult↗
PubMed1989

Mate guarding as paternity insurance in Idaho ground squirrels.

Following a copulation, males in many species of vertebrates (particularly birds) and invertebrates remain near the inseminated female and repel other suitors with displays or force. Guarding males must delay resumption of competitive mate searching, but they may insure their paternity by reducing possibilities for secondary matings and sperm competition. Among mammals, post-copulatory mate guarding has been reported in rodents, mongooses, ungulates and primates, including humans, but the effects of such behaviour on male reproductive success have not been determined genetically. I report here that mate guarding by male Idaho ground squirrels (Spermophilus brunneus) enhances a male's probability of paternity. Furthermore, an analysis based on game theory shows that mate guarding is an evolutionarily stable strategy for male S. brunneus, but not male Belding's ground squirrels (S. beldingi), which resume searching once copulation is completed.

Animals↗
PubMed1976

Uni-directional growth of F-actin.

In was shown that the growth of F-actin occurs uni-directionally in vitro; that is, actin monomers (G-ADP-actin) polymerize onto only one of the two ends of a pre-existing seed in the absence of ATP. Fragments of the F-actin-heavy meromyosin complex prepared by sonication were used as seeds. By studying a large number of electron micrographs, we concluded that growth occurs on the tail end of the arrow-head structure of the seed. This result suggests that the thin filament grows in vivo from the center of the sarcomere towards the Z-line. It was further shown that the fragments of F-actin combine with both ends of the seed with nearly equal probability. These results are well interpreted according to the theory developed by Oosawa (1,2).

Actins↗
PubMedDate not supplied

The menisci of the lumbar zygapophyseal joints. A review of their anatomy and clinical significance.

The literature describing menisci in the lumbar zygapophyseal joints is reviewed. The only true menisci in these joints are rudimentary fibrous invaginations of the dorsal and ventral capsule. So-called menisci at the superior and inferior poles of the joint are basically fat-filled synovial reflections, some of which contain dense fibrous tissue, which probably arises as a result of mechanical stress. The theory of meniscus entrapment is appraised, but is considered to have been an overstated cause of those forms of "acute locked back" that responds to manipulation.

Adipose Tissue↗
PubMed1989

Framing of information: its influence upon decisions of doctors and patients.

Prospect theory postulates that decisions are influenced not only by probability and value of possible outcomes, but also by the manner in which these probabilities are presented. Variations in the presentation of the same information, in several areas of care, are considered to determine their influence upon health decisions of both doctors and patients. Three health-related predicaments involving varying levels of risk are presented either in a positive or a negative frame and were given to 74 medical students who stated whether they would advise a patient or be prepared themselves to undergo one of three medical procedures. The influence of framing upon these decisions was evident both when subjects responded as patients and as doctors, but its influence was bounded by the level of risk and the type of health decision. These findings raise questions concerning how probabilistic information should be presented to both patients and doctors to counteract the effect of framing upon their decisions.

Attitude to Health↗
PubMed1988

Analysis of the 'epidemic' of multiple sclerosis in the Faroe Islands. II. Biostatistical aspects.

A series of biostatistical tests were applied to the data upon which the Faroe epidemic hypothesis was constructed. Temporal, cluster analysis using three commonly applied methods were unsuitable because of the very small size of the sample (32 cases of MS). Methods to detect non-random clusters of disease identified a cluster of 16 cases with date of onset between 1941-1950 (p less than 0.05). However, when 1 questionable case of MS was excluded, the resulting cluster did not support the epidemic hypothesis. The overlapping 95% confidence limits of 5- and 10-year based incidence rates of MS, by date of onset (Poisson distribution) argues against the presence of an epidemic. Analysis of the exposure data, i.e. contacts between the Faroese and the British troops, yielded only borderline statistical significance but changing a single case of MS from the exposed to the unexposed category failed to support the exposure theory. All calculations were also carried out using the probable date of acquisition of the disease, between the ages of 5 and 14 years; these also failed to substantiate the hypotheses of epidemic and transmissibility. Since the validity of statistical analysis to test for the presence of epidemics with small sample sizes is not well established, the lack of concordance between the results of the various approaches leads to the conclusion that there was no epidemic of MS in the Faroes.

Adolescent↗
PubMed2001

[Development of theme in radiochemistry].

The disintegration rates of 222Rn and its daughters in natural water were determined successfully by the use of the integral counting method with a liquid scintillation spectrometer. A significant advantage of this method is its freedom from the quenching effect. Moreover, when plural alpha-, and beta-emitters are present, their total amounts can be determined. The simple extrapolation of integral counting curve to zero pulse-height, however, do not give the true disintegration rate for the soft beta-emitters (Emax < 200 keV), because the liquid scintillator (LS) has a relatively high detection threshold. Therefore, the zero detection threshold of the liquid scintillation spectrometer was determined by measuring standard 3H samples, and a modified integral counting method which extrapolates the integral counting curve to the zero detection threshold was proposed. The method has been successfully applied to various beta-emitters, 222Rn samples, and coloured samples of beta-emitters, giving more accurate absolute disintegration rate than the conventional integral counting method and the efficiency tracing method. In the course of the study determining 222Rn by liquid scintillation counting, we observed unexpected phenomena; the air luminescence from gaseous space above LS, and the temperature dependence of pulse-height spectra. As for the former phenomenon, we proposed a method for correcting errors due to air luminescence, a method for determining alpha-emitters by the air luminescence, and a rapid calibration method for 222Rn detectors. As for the latter phenomenon, we observed that the pulse-height spectra for alpha, and beta-emitters in LS are shifted toward higher pulse-height with decreasing temperature. We found that the fluorescence intensities of the solvent of LS (toluene) is promoted at lower temperatures, and that not only toluene, but also the fluorescence intensity of a number of aromatic hydrocarbons and aliphatic hydrocarbons show the same effect as toluene. Other unexpected results are existence of metals in number of enzymes, and discrepancies between the experimental value for Kurie plot of allowed beta-emitters and the value which would be expected according to Fermi's theory, the results of which would affect the transmission probability of potential barrier for alpha-particles.

Fluorescence↗