Improvement of in-situ gamma spectrometry methods by Monte-Carlo simulations

Publication date: Available online 10 November 2017
Source:Journal of Environmental Radioactivity
Author(s): Dusan Mrdja, Kristina Bikit, Sofija Forkapic, Istvan Bikit, Jaroslav Slivka, Jan Hansman
Performing in-situ measurements of gamma radiation originating from soil requires adequate detection efficiency curves, which can be obtained by Monte-Carlo simulations. In simulations, soil density of 1.046 g/cm³ was used, with the following elemental composition of soil in which gamma radiation was generated: O - 47%, Si −35%, Al - 8%, Fe - 3.9%, C - 2.1%, Ca - 1.4%, K - 1.3%, N - 0.6%, Mg - 0.6%, N - 0.1%. Soil matrix was represented by cylindrical volume of 1.5 m diameter and 0.5m thickness, while germanium detector was placed at 1 m height above the soil. The simulated gamma spectrum, originated from K-40, as well as from members of Th-232 chain, and daughters of Ra-226, was obtained. Homogeneous distribution of various radionuclides (Ra-226, Th-232, K-40) in soil matrix is considered in this work. Gamma spectra obtained in simulations were analyzed, and together with simulated detection efficiency data they provide comparison with real experimental measurements and practical application of results derived by Monte-Carlo simulations. As a result of this work, the corresponding detection efficiency curve for HPGe detector was obtained, which can be applied for in-situ measurements of radionuclide concentration in soil, assuming uniform radionuclide distribution.In order to validate our simulation results regarding detection efficiency, we performed in-situ measurements of soil radioactivity and compared the obtained activity concentrations with laboratory measurements. We found a good agreement, within activity concentration uncertainty, between in-situ measurement results and average values of activity concentrations obtained by laboratory measurements.



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UBC-Nepal expedition: acclimatization to high-altitude increases spinal motoneurone excitability during fatigue in humans

Abstract

The fatigue-induced failure of the motor cortex to drive muscles maximally increases in acute hypoxia (AH) compared to normoxia (N) but improves with acclimatization (chronic hypoxia; CH). Despite their importance to muscle output, it is unknown how locomotor motoneurones in humans are affected by hypoxia and acclimatization. Eleven participants performed 16 min of submaximal (25% maximal torque, MVC) intermittent isometric elbow flexions in N, AH (environmental chamber), and CH (7–14 days at 5050 m) (P_IO_2 = 140, 74, and 76 mmHg, respectively). Each minute of the fatigue protocol, motoneurone (MN) responsiveness was measured with cervicomedullary stimulation delivered 100 ms after transcranial magnetic stimulation (TMS) used to transiently silence voluntary drive. Every two minutes, cortical voluntary activation (cVA) was measured with TMS. After the task, MVC torque declined more in AH (∼20%) than N and CH (∼11 and 14%, respectively, P < 0.05), with no differences between N and CH. cVA was lower in AH than N and CH at baseline (∼92, 95, 95%, respectively) and the end of the protocol (∼82, 90, 90%, P < 0.05). During the fatiguing task, MN excitability in N and AH declined to ∼65 and 40% of the baseline value (P < 0.05). In CH, MN excitability did not decline and, late in the protocol, was ∼40% higher compared to AH (P < 0.05). These novel data reveal that acclimatization to hypoxia leads to a heightened motoneurone responsiveness during fatiguing exercise. Positive spinal and supraspinal adaptations during extended periods at altitude might therefore play a vital role for the restoration of performance after acclimatization to hypoxia.

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Mechanisms underpinning sympathetic nervous activity and its modulation using transcutaneous vagus nerve stimulation

Abstract

The autonomic nervous system, consisting of the sympathetic and parasympathetic branches, is a major contributor to maintaining cardiovascular variables within homeostatic limits. As we age or in certain pathological conditions, the balance between the two branches changes such that sympathetic activity is more dominant and this change in dominance negatively correlates with prognosis in conditions such as heart failure. We have shown that non-invasive stimulation of the tragus of the ear increases parasympathetic activity and reduces sympathetic activity and that extent of this effect is correlated with the baseline cardiovascular parameters of different subjects. The effects could be due to activation of the afferent branch of the vagus and potentially other sensory nerves in that region. This indicates that tragus stimulation may be a viable treatment in disorders where autonomic activity to the heart is compromised.

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Liver X receptor activation inhibits SGLT2-mediated glucose transport in human renal proximal tubular cells

Abstract

Liver X receptors (LXRs) are members of a nuclear receptor family consisting of two isoforms, LXR-α and LXR-β. They play a major role in energy metabolism including lipid and glucose metabolism. Recent studies reported LXRs regulate plasma glucose although the mechanism is still uncertain. The present study investigated whether LXR activation regulates sodium glucose cotransporter2 (SGLT2) in human renal proximal tubular cells. LXR agonists, T0901317 and GW3965, inhibited SGLT2-mediated glucose uptake in concentration-dependent manners. The effect of T0901317 and GW3965 was attenuated by a LXR antagonist, fenofibrate. Activation of retinoid X receptor (RXR) agonist, bexarotene, potentiates the inhibitory effect of these ligands. Thus, the inhibitory effect of LXR agonists on SGLT2 was mediated and facilitated by LXR and RXR activation, respectively. In addition, the inhibitory effect of LXR agonists was not mediated by cytotoxicity. Exposing HK-2 cells, renal proximal tubular cell line, to LXR agonists significantly reduced the maximal transport rate (J_max) of SGLT2 without any effect on transporter affinity. Western blot analysis revealed LXR activation significantly decreased protein expression of SGLT2 with no change in mRNA level. In addition, LXR activation inhibited canagliflozin-sensitive short-circuits current which represents SGLT2-mediated glucose transport in polarized human renal proximal tubular cell monolayer. Furthermore, LXR activation inhibited transport function of SGLT2 in hyperglycemic conditions. As such, this study represents the evidence of LXR activation's inhibitory effect on glucose transport in human renal proximal tubular cells.

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The Effect of Natural or Simulated Altitude Training on High-Intensity Intermittent Running Performance in Team-Sport Athletes: A Meta-Analysis

Abstract

Background

While adaptation to hypoxia at natural or simulated altitude has long been used with endurance athletes, it has only recently gained popularity for team-sport athletes.

Objective

To analyse the effect of hypoxic interventions on high-intensity intermittent running performance in team-sport athletes.

Methods

A systematic literature search of five journal databases was performed. Percent change in performance (distance covered) in the Yo-Yo intermittent recovery test (level 1 and level 2 were used without differentiation) in hypoxic (natural or simulated altitude) and control (sea level or normoxic placebo) groups was meta-analyzed with a mixed model. The modifying effects of study characteristics (type and dose of hypoxic exposure, training duration, post-altitude duration) were estimated with fixed effects, random effects allowed for repeated measurement within studies and residual real differences between studies, and the standard-error weighting factors were derived or imputed via standard deviations of change scores. Effects and their uncertainty were assessed with magnitude-based inference, with a smallest important improvement of 4% estimated via between-athlete standard deviations of performance at baseline.

Results

Ten studies qualified for inclusion, but two were excluded owing to small sample size and risk of publication bias. Hypoxic interventions occurred over a period of 7–28 days, and the range of total hypoxic exposure (in effective altitude-hours) was 4.5–33 km h in the intermittent-hypoxia studies and 180–710 km h in the live-high studies. There were 11 control and 15 experimental study-estimates in the final meta-analysis. Training effects were moderate and very likely beneficial in the control groups at 1 week (20 ± 14%, percent estimate, ± 90% confidence limits) and 4-week post-intervention (25 ± 23%). The intermittent and live-high hypoxic groups experienced additional likely beneficial gains at 1 week (13 ± 16%; 13 ± 15%) and 4-week post-intervention (19 ± 20%; 18 ± 19%). The difference in performance between intermittent and live-high interventions was unclear, as were the dose of hypoxia and inclusion of training in hypoxia.

Conclusions

Hypoxic intervention appears to be a worthwhile training strategy for improvement in high-intensity running performance in team-sport athletes, with enhanced performance over control groups persisting for at least 4 weeks post-intervention. Pending further research on the type of hypoxia, dose of hypoxia and training in hypoxia, coaches have considerable scope for customising hypoxic training methods to best suit their team's training schedule.

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Heat Acclimation Decay and Re-Induction: A Systematic Review and Meta-Analysis

Abstract

Background

Although the acquisition of heat acclimation (HA) is well-documented, less is known about HA decay (HAD) and heat re-acclimation (HRA). The available literature suggests 1 day of HA is lost following 2 days of HAD. Understanding this relationship has the potential to impact upon the manner in which athletes prepare for major competitions, as a HA regimen may be disruptive during final preparations (i.e., taper).

Objective

The aim of this systematic review and meta-analysis was to determine the rate of HAD and HRA in three of the main physiological adaptations occurring during HA: heart rate (HR), core temperature (T _c), and sweat rate (SR).

Data Sources

Data for this systematic review were retrieved from Scopus and critical review of the cited references.

Study Selection

Studies were included when they met the following criteria: HA, HAD, and HRA (when available) were quantified in terms of exposure and duration. HA had to be for at least 5 days and HAD for at least 7 days for longitudinal studies. HR, T _c, or SR had to be monitored in human participants.

Study Appraisal

The level of bias in each study was assessed using the McMaster critical review form. Multiple linear regression techniques were used to determine the dependency of HAD in HR, T _c, and SR from the number of HA and HAD days, daily HA exposure duration, and intensity.

Results

Twelve studies met the criteria and were systematically reviewed. HAD was quantified as a percentage change relative to HA (0% = HA, 100% = unacclimated state). Adaptations in end-exercise HR decreased by 2.3% (P < 0.001) for every day of HAD. For end-exercise T _c, the daily decrease was 2.6% (P < 0.01). The adaptations in T _c during the HA period were more sustainable when the daily heat exposure duration was increased and heat exposure intensity decreased. The decay in SR was not related to the number of decay days. However, protracted HA-regimens seem to induce longer-lasting adaptations in SR. High heat exposure intensities during HA seem to evoke more sustained adaptations in SR than lower heat stress. Only eight studies investigated HRA. HRA was 8–12 times faster than HAD at inducing adaptations in HR and T _c, but no differences could be established for SR.

Limitations

The available studies lacked standardization in the protocols for HA and HAD.

Conclusions

HAD and HRA differ considerably between physiological systems. Five or more HA days are sufficient to cause adaptations in HR and T _c; however, extending the daily heat exposure duration enhances T _c adaptations. For every decay day, ~ 2.5% of the adaptations in HR and T _c are lost. For SR, longer HA periods are related to better adaptations. High heat exposure intensities seem beneficial for adaptations in SR, but not in T _c. HRA induces adaptations in HR and T _c at a faster rate than HA. HRA may thus provide a practical and less disruptive means of maintaining and optimizing HA prior to competition.

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Pliocene crocodiles from Kanapoi, Turkana Basin, Kenya

Publication date: Available online 11 November 2017
Source:Journal of Human Evolution
Author(s): Christopher A. Brochu
Three crocodylid species are known from the Pliocene Kanapoi locality in the western Turkana Basin. One of these, Crocodylus thorbjarnarsoni, includes material previously referred to Crocodylus niloticus (the modern Nile crocodile currently living in Lake Turkana) and Rimasuchus lloydi. C. thorbjarnarsoni was a gigantic horned crocodile similar in overall shape to most other generalized crocodylids, but its closest known relative is another extinct species, Crocodylus anthropophagus from the Pleistocene of Olduvai Gorge in Tanzania. It is not closely related to C. niloticus. The second is an extinct form of sharp-nosed crocodile (Mecistops), a group of slender-snouted crocodylids currently restricted to western and central Africa. The third is Euthecodon, a crocodylid with an extremely long, slender, and distinctively notched snout. Euthecodon and C. thorbjarnarsoni are known from substantial numbers of specimens, but only one Mecistops specimen has been identified from the locality. The crocodylian fauna at Kanapoi is taxonomically similar to that of most other Plio-Pleistocene fluviolacustrine deposits in the Turkana Basin. Crocodylian diversity in the Turkana region contracted from a peak of five co-existing species in the late Miocene to one today; this contraction was underway by the early Pliocene, but crocodylian diversity remained stable at three species until well into the Quaternary.



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