Perched Ponds: An Arctic Variety

Data obtained during several seasons of field research on a small drainage basin in the Colville River delta of northern Alaska were used in a study of permafrost as an aquaclude for the maintenance of a pond above the regional water table. The development of the active layer of permafrost in the basin and the water budget of the pond were monitored. It was shown that the permafrost table enables the general form of the basin's subaerial surface to be maintained throughout the thaw season. The resulting prevention of percolation, when combined with a low evaporation rate, is sufficient to ensure that the pond is perennial

Event-related potentials in autistic and healthy children on an auditory choice reaction time task

Introduction: Childhood autism can occur in 5 out of 10,000 of the population. The condition covers problems of sensory modulation, comprehension and communication as it relates to both objects and people. Of the stages of information processing recorded in auditory event-related potentials (ERPs), reductions of N1 and P3 amplitude have been reported in many situations, but an increased P3 response to non-targets may represent difficulties in attributing differentially significance to some but not all stimuli.. Methods: Recordings were derived from midline and 4 lateral sites on the scalp of 7 children with autism and 7/13 healthy control children matched for age (median 139 vs. 135 months). A three-tone oddball paradigm was presented in a passive and active-task form (72% at 1 kHz, 14% at 0.5 kHz and 14% at 2.0 kHz) Results: a) Autistic subjects showed twice as many errors of omission and a higher beta criterion (signal detection) for targets. b) For autistic subjects N1 latencies were shorter and N1 amplitude larger to deviants (especially nontargets). c) However, subtraction of the ERPs in nontarget from target conditions showed that the processing negativity (PN) and especially the Negative difference (Nd) was smaller in autistic subjects. d) In contrast the P3 amplitude (especially after the target) was smaller in autistic subjects. e) Within autistic subjects the topography showed more early negativity after deviants at left frontal sites and more target induced late positivity at right parietal sites. Conclusions: The ERPs of autistic children were more responsive to stimulus features (high frequency or deviance) and less responsive to the stimulus associations (target features). The ERPs also provide conflicting signs of neurodevelopment, -- precocious in the right-hemispheric emphasis for P3, but delayed in that P3 was not maximal at parietal sites

Event-related potentials and monoamines in autistic children on a clinical trial of fenfluramine

Introduction: As autistic persons have problems with selecting and encoding meaningful stimuli and multi-centre studies (Ritvo et al., 1983, 1986) had reported mild behavioural improvements following treatment with fenfluramine, event-related potential (ERP) stages of information processing were studied in childhood autism as part of a double blind crossover study of the efficacy of dl fenfluramine. . Methods: Acceptable recordings were derived from midline and 4 lateral sites on the scalp of 7 from 14 young persons with autism who understood the task (6 male, 1 female 5.8-17.7 years-of-age). A three-tone oddball paradigm was presented in a passive and active-task form (72% at 1 kHz, 14% at 0.5 kHz and 14% at 2.0 kHz) under placebo and drug conditions (where each condition lasted 5 months). Eleven patients provided blood and urine samples for monoamine analyses in both conditions. Results: a) With fenfluramine treatment blood serotonin decreased and urinary catecholamine levels fell (25-45%, but dopamine utilization (HVA/DA) increased 2-4-fold. b) Under fenfluramine autistic subjects responded non-significantly faster, with fewer errors of omission and improved /decreased beta criterion (signal detection). [IQ measures increased 7.5 points.] c) N1 amplitudes (Fz) decreased and latencies increased in the fenfluramine condition. Early negativity (especially on the right) correlated inversely with HVA/DA actvivity. Subtraction of the ERPs in nontarget from target conditions showed that the Negative difference (Nd) increased during fenfluramine treatment. d) P3 amplitudes (especially after the deviants) increased with fenfluramine treatment. But in the difference waveform (active-minus-passive condition) the P3 amplitude was halved. The distribution of the P3 component moved rostrally with treatment. Conclusions: N1 and P3 components of the ERP were responsive to fenfluramine treament. Treatment appears to have mildly improved early stimulus processing at stages represented by the early negative components, but to have mildly impaired processing at the P3-stage. The N1 / Nd - related improvement seems to be related to increased dopamine activity (cf. neuroleptic-like properties of racemate fenfluramine)

Dietary omega-3 polyunsaturated fatty acids prevent vascular dysfunction and attenuate cytochrome P4501A1 expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) found in fish protect against cardiovascular morbidity and mortality; however, many individuals avoid fish consumption due to concerns about pollutants. We tested the hypothesis that n-3 PUFAs would prevent vascular dysfunction induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). C57Bl/6 male mice were fed a chow or n-3 PUFA diet for 10 weeks and were exposed to vehicle or 300 ng/kg/d TCDD during the final 2 weeks on each diet. Aortic vasoconstriction mediated by arachidonic acid (AA) +/- SKF525 (P450 inhibitor) or SQ29548 (thromboxane/prostanoid (TP) receptor antagonist) was assessed. RBC fatty acids and expression of n-3 and n-6 PUFA metabolites were analyzed. Cytochrome P4501A1 (CYP1A1), CYP1B1, and aryl hydrocarbon receptor (AHR) expression was measured. TCDD significantly increased AA-mediated vasoconstriction on a chow diet by increasing the contribution of P450s and TP receptor to the constriction response. In contrast, the n-3 PUFA diet prevented the TCDD-induced increase in AA vasoconstriction and normalized the contribution of P450s and TP receptor. While TCDD increased the levels of AA vasoconstrictors on the chow diet, this increase was prevent by the n-3 PUFA diet. Additionally, the n-3 PUFA diet significantly increased the levels of n-3 PUFA-derived vasodilators and TCDD increased these levels further. Interestingly, the n-3 PUFA diet significantly attenuated CYP1A1 induction by TCDD without a significant effect on AHR expression. These data suggest that n-3 PUFAs can prevent TCDD-induced vascular dysfunction by decreasing vasoconstrictors, increasing vasodilators, and attenuating CYP1A1 induction, which has been shown previously to contribute to TCDD-induced vascular dysfunction

Nitrogen pair-induced temperature insensitivity of the band gap of GaNSb alloys

The temperature dependence of the band gap of GaN x Sb1−x films with x ≤ 1.3% has been studied in the 1.1–3.3 m (0.35–1.1 eV) range using infrared absorption spectroscopy between 4.2 and 300 K. As with other dilute nitride semiconductors, the temperature dependence of the band gap is reduced by alloying with nitrogen when compared to the host binary compound. However, for GaNSb, the smallest variation of the band gap with temperature is observed for samples with the lowest N content for which the band gap is almost totally insensitive to temperature changes. This contrasts with the more widely studied GaN x As1−x alloys in which the band gap variation with temperature decreases with increasing N content. The temperature-dependent absorption spectra are simulated within the so-called band anticrossing model of the interaction between the extended conduction band states of the GaSb and the localized states associated with the N atoms. The N next-nearest neighbor pair states are found to be responsible for the temperature insensitivity of the band gap of the GaNSb alloys as a result of their proximity to the conduction band edge giving them a more pronounced role than in GaNAs alloys

Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model

Two approaches for analysis of pion photo- and electroproduction on nucleons in the resonance energy region are checked at $Q^2=0$ using the results of GWU(VPI) partial-wave analysis of photoproduction data. The approaches are based on dispersion relations and unitary isobar model. Within dispersion relations good description of photoproduction multipoles is obtained up to $W=1.8 GeV$. Within unitary isobar model, modified with increasing energy by incorporation of Regge poles, and with unified Breit-Wigner parametrization of resonance contributions, good description of photoproduction multipoles is obtained up to $W=2 GeV$.Comment: 23 pages, LaTe

New empirical fits to the proton electromagnetic form factors

Recent measurements of the ratio of the elastic electromagnetic form factors of the proton, G_Ep/G_Mp, using the polarization transfer technique at Jefferson Lab show that this ratio decreases dramatically with increasing Q^2, in contradiction to previous measurements using the Rosenbluth separation technique. Using this new high quality data as a constraint, we have reanalyzed most of the world e-p elastic cross section data. In this paper, we present a new empirical fit to the reanalyzed data for the proton elastic magnetic form factor in the region 0 < Q^2 < 30 GeV^2. As well, we present an empirical fit to the proton electromagnetic form factor ratio, G_Ep/G_Mp, which is valid in the region 0.1 < Q^2 < 6 GeV^2

A controlled crossover trial of fendluramine in autism

Introduction: Against a background of variable results achieved by the treatment of childhood autism with dopaminergic agonists or antagonists, and opiate antagonists and mild behavioural improvements achieved following treatment with fenfluramine (Geller et al., 1982; Ritvo et al., 1984 among others) a 12 month double-blind crossover trial of fenfluramine was undertaken. [the d-isomer releases serotonin, the l-isomer modestly blocks dopamine receptors.] Methods: Six female and 14 male children and adolescents with autism were enrolled (median 9y; range 5-17 years of age) in a trial run over a 1 month baseline, 5 months of treatment, 2 months placebo, and 5 months of treatment. Parent diaries were kept. Various tests and rating scales for development, verbal and noverbal abilities along with measures of blood serotonin, urinary catecholamines and auditory event-related potentials (ERPs) were measured at 6-month intervals. Results: a) With fenfluramine treatment children lost weight, blood serotonin decreased by 60% and urinary catecholamine levels fell (25-45%, but dopamine utilization (HVA/DA) increased 2-4-fold. b) Under fenfluramine some autistic subjects improved on measures of cognitive and language function. Two mute subjects began to speak, but for the group overall the improvements did not prove significant. [British Ability Scale, Reynell developmental language and Vineland social maturity scale improvements were significant.] c) Treatment improved early stages of information processing, but impaired later stages as measured in the ERP (i.e. early negative going excitatory vs. later positive going inhibitory response, respectively in 7 patients). The early negativity changes (especially over the right hemisphere) correlated inversely with HVA/DA actvivity. d) Side effects reported included lethargy and irritability.. Conclusions: While individuals showed marked reductions of stereotypies, hyperactivity, and improvements on develepmental and cognitive measures, the absence of clear group-wide effects suggests that fenfluramine would have but a limited place in the management of some patients with autism

Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors

Nucleon electromagnetic form factor data (including recent data) is fitted with models that respect the confinement and asymptotic freedom properties of QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson pole contributions and at high momentum transfer conform to the predictions of perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also include the width of the rho meson and the addition of higher mass vector meson exchanges, but do not evolve into the explicit form of PQCD at high momentum transfer. Different parameterizations of the GK model's hadronic form factors, the effect of including the width of the rho meson and the addition of the next (in mass) isospin 1 vector meson are considered. The quality of fit and the consistency of the parameters select three of the combined HP/GK type models. Projections are made to the higher momentum transfers which are relevant to electron-deuteron experiments. The projections vary little for the preferred models, removing much of the ambiguity in electron-nucleus scattering predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure, minor textual changes; email correspondence to [email protected]

Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors

The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in which the rho, omega, and phi vector meson pole contributions evolve at high momentum transfer to conform to the predictions of perturbative QCD (pQCD), was recently extended to include the width of the rho meson by substituting the result of dispersion relations for the pole and the addition of rho' (1450) isovector vector meson pole. This extended model was shown to produce a good overall fit to all the available nucleon electromagnetic form factor (emff) data. Since then new polarization data shows that the electric to magnetic ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En} data in their range of momentum transfer. The model is further extended to include the omega' (1419) isoscalar vector meson pole. It is found that while this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can fit the new R_p and R_n well simultaneously. An excellent fit to all the remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted. The model predictions are shown up to momentum transfer squared, Q^2, of 8 GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to [email protected] ; minor typos corrected, figures added, conclusions extende