First Results from the DEAP-3600 Dark Matter Search with Argon at SNOLAB.

This Letter reports the first results of a direct dark matter search with the DEAP-3600 single-phase liquid argon (LAr) detector. The experiment was performed 2 km underground at SNOLAB (Sudbury, Canada) utilizing a large target mass, with the LAr target contained in a spherical acrylic vessel of 3600 kg capacity. The LAr is viewed by an array of PMTs, which would register scintillation light produced by rare nuclear recoil signals induced by dark matter particle scattering. An analysis of 4.44 live days (fiducial exposure of 9.87 ton day) of data taken during the initial filling phase demonstrates the best electronic recoil rejection using pulse-shape discrimination in argon, with leakage <1.2×10^{-7} (90% C.L.) between 15 and 31 keV_{ee}. No candidate signal events are observed, which results in the leading limit on weakly interacting massive particle (WIMP)-nucleon spin-independent cross section on argon, <1.2×10^{-44} cm^{2} for a 100 GeV/c^{2} WIMP mass (90% C.L.).

Aminopyridine lengthened the plateau phase of action potentials in mouse sinoatrial node cells.

Duration of the plateau phase (phase 2) of action potentials in pacemaker cells in mouse sinoatrial node characterized by low upstroke rate during the rapid depolarization (dV/dt max <7 V/sec, phase 0) and in atrial-like cells with dV/dt max <100 V/sec were prolonged by 50% with 4-aminopyridine in concentrations of 0.7 and 0.1 mM, respectively. This blocker did not lengthen the terminal repolarization (phase 3). The above changes were accompanied by a 20-80% decrease in dV/dt max in comparison to the control. It is hypothesized that the short-term (transient) outward current Ito takes a part in the plateau formation and modulates the duration of the rapid depolarization phase of action potentials in mouse sinoatrial node cells.

The negative chronotropic effect of Cs(+) ions on generation of transmembrane potentials in mouse sinoatrial node cells.

Experiments on spontaneously contracting strips from sinoatrial region of the hearts of 2-month-old albino mice showed that cesium (Cs(+)), a blocker of hyperpolarization-activated I(f) current, in a concentration of 1 mM produced the greatest negative chronotropic effect on the duration of diastolic depolarization phase (75%), its rate (59%), and action potential duration (29%). The threshold concentration of Cs(+) was approximately 0.15 mM. In a concentration of about 8.5 mM, spontaneous generation of action potentials stopped. The effect was reversible. Thus, blockade of I(f) current by Cs(+) reduced the rate of action potential generation in cells of mouse sinoatrial node by app. 42% in comparison with controls.

[A differentiated approach to the diagnosis and treatment of portal hypertension in children].

The authors analyze their experience with diagnosis and treatment of 182 children with syndrome of portal hypertension (PH) from 1991 through 2010. Two groups of patients were considered. The first group included 74 newborns with high risk of the development of PH (infants after catheterization of the umbilical vein who endured omphalitis with USI diagnosed thrombosis of the portal vein, patients with cavernous transformation of the portal vein, hepatosplenomegaly). The second group consisted of 108 children aged from 6 months to 14 years with realized syndrome of PH. Investigation of hemostasis (international normalized ratio, fibrinogen, VIII and IX factors) immunogram of the 2nd level, determination of gene polymorphism (prothrombin, V factor, MTHFR, PAI-1), Bonacini index were included in the complex of examination, besides clinical and biochemical analyses of blood. The degree of disturbance of hemodynamics in the portal system was estimated by the data of USI, dopplerography, FEGS. It was established that children with extrahepatic portal hypertension have markers of hereditary thrombophilia in 98% of cases. Bonacini index allows determination of early signs of the development of secondary fibrosis of the liver in children with PH without using liver biopsy.

Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data.

The DEAP-3600 detector searches for the scintillation signal from dark matter particles scattering on a 3.3 tonne liquid argon target. The largest background comes from 39 Ar beta decays and is suppressed using pulse-shape discrimination (PSD). We use two types of PSD estimator: the prompt-fraction, which considers the fraction of the scintillation signal in a narrow and a wide time window around the event peak, and the log-likelihood-ratio, which compares the observed photon arrival times to a signal and a background model. We furthermore use two algorithms to determine the number of photons detected at a given time: (1) simply dividing the charge of each PMT pulse by the mean single-photoelectron charge, and (2) a likelihood analysis that considers the probability to detect a certain number of photons at a given time, based on a model for the scintillation pulse shape and for afterpulsing in the light detectors. The prompt-fraction performs approximately as well as the log-likelihood-ratio PSD algorithm if the photon detection times are not biased by detector effects. We explain this result using a model for the information carried by scintillation photons as a function of the time when they are detected.

Characterization of changes in the configuration of action potentials in the mouse, guinea pig, and pig sinoauricular node after application of channel blockers of the rapid and slow delayed rectifier potassium currents.

We hypothesized that the repolarization phase of action potentials (APs) in mammals with large body mass and high cardiac output could not be reliably controlled by only one of the delayed rectifier potassium IK current components. To test this hypothesis experimentally, we performed a comparative study of the response of AP phases to the rapid IKr channels blocker E-4031 and slow IKs blocker chromanol 293B in APs spontaneously generated in strips of sinoauricular (SA) tissue from mouse, guinea pig, and pig hearts. Application of a slow channels blocker chromanol 293B caused a decrease of Aps generation frequency in SA area strips from mouse, guinea-pig and pig by 5.3, 16, and 18% compared to the control. Treatment with the IKr blocker E-4031 caused a significant reduction of APs generation frequency in the mouse, guinea pig, and pig SA strips by 24, 26, and 36%, respectively, compared to the control values. These results suggest that the rapid IKr current is the key component responsible for AP generation in sinoauricular node cells of the pig heart.

Growth of aligned carbon nanofibres over large areas using colloidal catalysts at low temperatures.

Highly purified cobalt colloids have been employed as a catalyst to grow aligned carbon nanofibres at temperatures as low as 300 degree C by dc plasma enhanced chemical vapour deposition over large areas.

Modelling of the effects of Na+ and Ca2+ ions on the generation of action potentials by rabbit heart true pacemaker cells.

A comparison of results of modelling and physiological experiments allowed to estimate in the first approximation the quantitative contribution of calcium and sodium ions to the generation of different ionic currents determining the shape of the action potential (AP). Generally, the model reproduced adequately variations in AP shape with changes in the external concentrations of Na+ and Ca2+. At the same time the model differs slightly from the experimental results. To improve the model kinetic variables of slow inward current have to be taken into account.

Single and multiple early afterdepolarization caused by nickel in rat atrial muscle.

We examined the possible role of the Na-Ca exchange (NCX) in the arrhythmogenesis in rat atrial preparations applying microelectrode technique. In control Tyrode solution preparations isolated from the sinoatrial area contracted with frequency of 48+/-4 min(-1) (group I) or 84+/-7 min(-1) (group II). In preparation beating with low frequency partial inhibition of NCX by administration of Ni2+ (0.3 mmol/l) to the bath solution caused single early afterdepolarization (EAD) on the 15th min. During the following five minutes they were transformed into multiple EADs from 4 to 47 (action potentials) with general duration of 1-12 s. The effects were reversible. Ni2+ (0.3 mmol/l) in the preparations beating with higher rate (group II) did not cause multiple EADs, but after higher Ni2+ concentration (0.5 mmol/l) single EAD was observed more often. It was concluded that Ca2+ overload due to partial block of the NCX can contribute to the development of atrial tachyarrhythmias.

[Ultrastructural pathology of the placenta in respiratory-syncytial viral infection and mycoplasmosis]. / Ul'trastrukturnaia patologiia platsenty pri respiratorno-sintsitial'noi virusnoi infektsii i mikoplazmoze.

Electron microscopy of the placentas affected by respiratory-syncytial virus and mycoplasmas (Mycoplasma urealyticum) revealed the most pronounced alterations in the syncytiotrophoblast structures. Destructive changes in the respiratory-syncytial infection were associated with a direct reproduction of viral particles. Two types of alterations (acute and long-lasting) reflecting two stages of the infectious process are reported in the Mycoplasma infection.

[Central nervous system lesions in fetuses and newborns in intrauterine infection caused by respiratory viruses]. / Porazheniia tsentral'noi nervnoi sistemy plodov i novorozhdennykh pri vnutriutrobnoi infektsii, vyzvannoi respiratornymi virusami.

Congenital respiratory viral infection is followed in the CNS of fetuses and newborns by grave dyscirculatory disturbances with glia proliferation and nervous tissue edema. The process is mainly localized in the periventricular regions of the brain ventricles. Neurologic and morphologic consequences of these damages in the CNS of fetuses and newborns need further studies.

[Effects of sodium and calcium ions on the potentials of cardiac pacemaker cells in the frog]. / Effekty ionov natriia i kal'tsiia na potentsialy kletok voditelia ritma serdtsa liagushki.

True and latent pacemaker cells were differentiated in the frog heart sino-atrial area. Within the first 5 min in the hyposodium solution, a decrease of the overshoot and maximal velocity of depolarization occurred. The true pacemaker cells did not reveal any changes of the AP parameters within 30-60 min. The cells of true pacemaker exhibited a higher sensitivity to the hypocalcium solution. The data obtained suggested a scheme of the whole cycle of Na+, K+ and Ca2+ exchange.

[The dispensary observation of patients with chronic nonspecific lung diseases who work in a dust-producing industry with a high radionuclide level as a consequence of the accident at the Chernobyl Atomic Electric Power Station]. / Dispansernoe nabliudenie za bol'nymi khronicheskimi nespetsificheskimi zabolevaniiami legkikh, rabotaiushchimi na pylevom proizvodstve s povyshennym soderzhaniem radionuklidov vsledstvie avarii na Chernobyl'skoi AES.

Patients working at a small mining institution and suffering of chronic unspecific pulmonary diseases due to high dust and radionuclide contamination levels were examined. Four groups of dispensarization were singled out with the purpose of differential treatment for each group. Such treatment including also antiaggregant agents, nitro-drugs resulted in a good medico-social effect within 2 years.

[Iridodiagnosis in the system of the follow-up of the health status of the population living in an area contaminated by radioactive substances]. / Iridodiagnostika v sisteme kontrolia za sostoianiem zdorov'ia naseleniia, prozhivaiushchego na territorii, zagriaznennoi radioaktivnymi veshchestvami.

The authors substantiate the practical employment of the iridodiagnosis screening-test using a system of archiving and visualization of the iris at the first stage of prophylactic medical examination and management. The economical and medical efficacy of the method has been established. Use of iridodiagnosis improved the detectability of pathologic conditions as compared with complex medical examination. Many specialists were freed from mass medical screening. The expenses for prophylactic medical examination became ten times less.

[The involvement of lidocaine and tetrodotoxin-sensitive current in the generation of action potentials with low DV/DT max in the cells of the mouse sinoauricular region].

The effects of the specific blockers of the inward Na-current --lidocaine and tetrodotoxin (TTX) were studied with microelectrode technique on the spontaneously beating strips of the mouse sinoauricular (SA) area. Lidocaine (25 microM) and TTX (25 pM) increased the duration of the peak of the action potentials (AP) of true pacemaker cells by extending the plateau phase (phase 2 or APD 20), slowing the dV/dt max from 2.6 +/- 0.8 V/s (n = 25) to 1.4 +/- 0.3 V/s (n = 5, p < 0.05) and reducing the velocity of diastolic depolarization (DD) by 20%. The extend of the dV/dt max value decline depended on the lidocaine concentration. The experimental data fully meted to Hill equation. The lidocaine threshold concentration was 20 microM. The lidocaine effective concentration which decreased dV/dt max by 50% (EC50) was 35 microM. The TTX (25 microM) exposure decreased the dV/dt max from 1.6 V/s to 0.8 V/s and DD velocity slowed by 49%. It should be noted that TTX also increased the duration of APD20. Our data show that dV/ dt max of the true pacemaker cells was reduced by 35-45% after exposure to TTX and lidocaine. This fact confirms the involvement of Na-current in the generation of the upstroke true pacemaker cells AP.

[Mechanism of outercellular [K+] in generation of pacemaker action potentials in sinoatrial valve of the rabbit].

In a control solution (solution I; 3 mM K+, 35 degrees C) the amplitude of APs of cells in the valve centre was 81 +/- 6 mV (Mean +/- SEM), the maximal upstroke velocity (dV/dtmax) was 19 +/- 4 V/s, velocity slow diastolic depolarization (DD) - 65 +/- 8 mV/s, the rate of spontaneous AP generation was 135 +/- 14 bpm. Hypo K+ (50 %) solution (solution II) decreased slow DD by - 22 % and dV/dtmax by -58 % and the rate of AP generation by 15 % compared to the control solution. In saline solution, decrease of Emax from -68 to -45 mV and four-fold decrease of slow DD and dV/dtmax were registered at the 8th of exposure. After that the Emax noise and origin of early (EADs) and delay (DADs) afterdepolarizations were observed. Comparative analysis of the main AP parameters of SA valve latent pacemaker cells in solution III (without K+) and solution IV (without KC1 and CaCl2) exposure demonstrated that changes of this parameters in solution IV were less then in solution III. It is interesting that in solution IV exposure the phase of the early repolarization (phase 1) was differentiated, dV/dtmax was increased by 21%. The frequency of AP generation decreased by 18 % as in solution with 50% K+. At the same time, EADs were not registered. It seems that the decreasing of the transsarcolemal gradient of K+ depolarized Emax despite Nernst equation. At the same time permeability was decreased for K+ and Na+ ions. That could involve Ca2+ overload and origin of EADs and DADs.

Tests of nuclear half-lives as a function of the host medium and temperature: refutation of recent claims.

When radioactive isotopes that decay by alpha, beta(-), beta(+) and electron-capture transitions are placed in a conducting host material, it has recently been claimed that their half-lives show a significant dependence on temperature-up to a 6% difference between room temperature and 12K. We have refuted two of these claims by measuring: (1) the beta(-) decay of (198)Au in gold, for which we find the half life to be the same within 0.04% between room temperature and 19K; and (2) the electron-capture decay of (97)Ru in ruthenium, for which we find any half-life difference to be <0.1%.