Cold Valleys Research Articles

Special Characteristics and Stability Analysis of Bank Slope Deposits with Special Geotechnical Structures in High and Cold Valleys

Due to the special internal and external dynamic action of the Qinghai-Tibet Plateau, the high and cold valleys are typically characterized by high-steep terrain, dry and cold climate, lithologic diversity, complex geological structure, and frequent occurrence of earthquakes. In this study, the types of special geotechnical structures of bank slope deposits in high and cold valleys are summarized based on field investigation, field and laboratory tests, and numerical simulation. These special deposits include colluvial-deluvial deposits, terrace deposits, early debris flow deposits, and landslide deposits. The formation mechanism, physical and mechanical properties, and stability analysis of these deposits were studied. The results show that the formation mechanism of various deposits is different, which is closely related to the intense geological tectonic action, the weathering and unloading action intensified by freezing and thawing cycles, and the special rock and soil structure in the high and cold valleys. Different material compositions have obvious effects on the physical and mechanical properties of the deposits, thus affecting the stability and deformation characteristics of the deposits. Under natural and saturated conditions, the stability of different types of the deposits is different, which is mainly related to the special geotechnical structure of various deposits. Compared with that before the reservoir impoundment, the stability factor of various deposits after the reservoir impoundment is significantly reduced. The performances can be provided as a reference for evaluating the stability of bank slope deposits in high and cold valleys.

Improved prediction of the vertical distribution of ground ice in Arctic-Antarctic permafrost sediments

Global warming and permafrost degradation are impacting landscapes, ecosystems and the climate-carbon system. Current ground ice and geohazard maps rely on the frost susceptibility of surficial sediments, and substantial areas underestimate ice abundance. Here we use a soil environmental model to show the importance of considering unfrozen water content (dependent on sediment type, soil water chemistry, and temperature) when assessing the frost susceptibility of sediments. Our ensemble modeling of the vertical structure and evolution of ground ice for fine to coarse-grained sediments matches reasonably well with field measurements at sites from the low Arctic to the cold and hyper-arid Dry Valleys of Antarctica. Our modeling indicates a need to re-evaluate how frost-susceptible sediments are identified when mapping ice-rich permafrost landscapes and provides a framework for the development of quantitative estimates of the vertical distribution of ground ice in permafrost sediments at regional scale.

Investigation of the cold valley paths for the synthesis of isotopes of Ubh in optimum orientations

Cold valley paths have been investigated for the synthesis of isotopes of superheavy element Unbihexium using quantum mechanical fragmentation theory, which suggests the fusion of fission fragments belonging to the cold valleys in the potential energy surfaces with at least one spherical closed shell nucleus as the reaction partner for the nuclear synthesis. For the suitability of the cold valley fission fragments for the synthesis of isotopes of Ubh, first the fragmentation potentials, preformation probabilities and fission barriers of the fission fragments of 314Ubh and 326Ubh compound systems in their ground states have been compared by keeping the fragments either in hot or cold optimum orientations. The comparison suggests 138Ba + 176Yb and 132Sn + 194Os reactions in hot optimum orientations for the synthesis of isotopes of Ubh due to their highest values of preformation probabilities, lowest values of the fragmentation potentials and relatively good values of the fission barriers. Also, the reactions 68Ni + 246Cf and 70Ni + 256Cf have been considered for the comparison with 138Ba + 176Yb and 132Sn + 194Os reactions due to their relatively smaller values of the Coulomb potential, higher mass-asymmetry and fission barrier, and shell closures next to 48Ca which has been used in most of the experiments for the synthesis of superheavy elements. Finally, the excitation functions for the neutron evaporation from the compound systems formed in these reactions, the probabilities of the formation and survival of the compound nuclei have been compared to suggest the suitable cold valley paths energies for the synthesis of the isotopes of Ubh.

Comparison and Selection of Thermal Insulation Materials for RCC Dam Construction in Dry and Cold Valleys at High Altitudes in Tibet

Effective temperature preservation and moisture retention measures are key techniques in ensuring concrete quality and preventing cracks formation in RCC dams and the concrete surface in the middle reaches of the Yarlung Tsangpo River in dry and cold river valleys. Insulation and moisture retention effect, construction technology, and cost of pasting polystyrene board, spraying foam polyurethane, and rubber plastic sponge insulation membrane on the dam concrete surface were compared and analyzed to determine the thermal insulation material with the best temperature preservation, best moisture retention effect, and high applicability. Finally, the rubber plastic sponge, which matched the trim strip process, was determined as the best insulation material. It features temperature preservation, moisture preservation, no secondary cleaning after removal, good appearance, and high secondary utilization rate. The results of dam overwintering monitoring and uncovering inspection in 2019 showed that the internal and external temperature differences and surface humidity indexes of concrete were within the design index value, and cracks were absent. The purpose of temperature control and crack prevention of dam concrete was achieved, and the material has high application value.

Systematic investigation of cluster radioactivity for uranium isotopes

The most probable cluster decays that can be observed for 217–238U isotopes are investigated. We identified the more-probable decays that commonly manifest themselves via cold valleys in the driving potentials with respect to the mass number and the atomic number, individually. The calculations are performed using the Skyrme-SLy4 nucleon–nucleon interaction, within the frame work of the performed cluster model. Among the indicated favored decays that involve emitted light clusters heavier than α-particle, twenty six decay modes display calculated half-life less than 1022 years, with branching ratio larger than 10−14%. The estimated branching ratio for the α-decay of 237U, that did not observed yet, is B=2.1×10−10% (Tα=8.7×109 years). The indicated most probable decays that did not observed yet include the 22Ne decay of 232U, 25Ne and 32Si decays of 233U, 24Ne and 29Mg decays of 235U, and the 34Si and 30Mg decay modes of 238U, with 10−14<B(%)<10−7.

Formation and decay of the compound nucleus Th*220 within the dynamical cluster-decay model

Background: The radioactive $^{220}\mathrm{Th}^{*}$ compound nucleus (CN) is of interest since the evaporation residue (ER) cross sections are available for various entrance channels $^{16}\mathrm{O}+^{204}\mathrm{Pb}$, $^{40}\mathrm{Ar}+^{180}\mathrm{Hf}$, $^{48}\mathrm{Ca}+^{172}\mathrm{Yb}$, and $^{82}\mathrm{Se}+^{138}\mathrm{Ba}$ at near barrier energies. Within the dynamical cluster-decay model (DCM), the radioactive CNs $^{215}\mathrm{Fr}^{*}$, $^{242}\mathrm{Pu}^{*}$, $^{246}\mathrm{Bk}^{*}$, and $^{254}\mathrm{Fm}^{*}$ are studied where the main decay mode is fission, with very small predicted ER cross section. $^{220}\mathrm{Th}^{*}$ provides a first case with experimentally observed ER cross section instead of fission.Purpose: To look for the optimum ``hot-compact'' target-projectile (t-p) combinations for the synthesis of ``cold'' $^{220}\mathrm{Th}^{*}$ and then its decay. For best fitting of the measured ER cross sections, with quasifission (qf) content, if any, the fusion-fission (ff) component is predicted. The magic-shell structure and entrance channel mass-asymmetry effects are analyzed, and the behavior of CN formation and survival probabilities ${P}_{\mathrm{CN}}$ and ${P}_{\mathrm{surv}}$ is studied.Methods: The quantum-mechanical fragmentation theory (QMFT) is used to predict the possible cold t-p combinations for synthesizing $^{220}\mathrm{Th}^{*}$, and the QMFT-based DCM is used to analyze its decay channels for the experimentally studied entrance channels. The only parameter of the model, the neck length $\mathrm{\ensuremath{\Delta}}R$, varies smoothly with the excitation energy ${E}^{*}$ of CN and is used to best fit the ER data and predict qf and ff cross sections.Results: The hot-compact and ``cold-elongated'' fragmentation paths show dissimilar results, whose comparisons with measured fission yields result in t-p combinations, the cold reaction valleys. For the decay process, the fixed $\mathrm{\ensuremath{\Delta}}R$ fit the measured ER cross section nicely, but not the individual decay-channel cross sections, which require the presence of qf effects, less so for asymmetric t-p combinations, and large (predicted) ff cross section.Conclusions: The calculated yields for hot-compact fragmentation path compared favorably with the observed asymmetric fission-mass distribution, resulting in mostly the same t-p reactions as are used in experiments. The best fitted $\mathrm{\ensuremath{\Delta}}R$ are found to be independent of the entrance channels, despite their very different cross sections, in conformity with our earlier works. The entrance-channel effects lead to the largest decay cross section for the most asymmetric and doubly magic t-p combination, the magicity taking over asymmetry for both the total ER and channel cross section. Furthermore, the variation of both ${P}_{\mathrm{CN}}$ and ${P}_{\mathrm{surv}}$ with ${E}^{*}$ fit in with the known systematic of other radioactive CN studied so far, thereby giving credence to our DCM analysis of $^{220}\mathrm{Th}^{*}$.

Systematic study of probable projectile-target combinations for the synthesis of the superheavy nucleus120302

Probable projectile-target combinations for the synthesis of superheavy element $^{302}$120 have been studied taking Coulomb and proximity potential as the interaction barrier. The probabilities of compound nucleus formation, PCN for the projectile-target combinations found in the cold reaction valley of $^{302}$120 are estimated. At energies near and above the Coulomb barrier, we have calculated the capture, fusion and evaporation residue cross sections for the reactions of all the probable projectile-target combinations so as to predict the most promising projectile-target combinations for the synthesis of SHE $^{302}$120 in heavy ion fusion reactions. The calculated fusion and evaporation cross section for the more asymmetric (hotter) projectile-target combination is found to be higher than the less asymmetric (colder) combination. It can be seen from the nature of quasi-fission barrier height, mass asymmetry, probability of compound nucleus formation, survival probability and excitation energy, the systems $^{44}$Ar + $^{258}$No, $^{46}$Ar + $^{256}$No, $^{48}$Ca + $^{254}$Fm, $^{50}$Ca + $^{252}$Fm, $^{54}$Ti + $^{248}$Cf, $^{58}$Cr + $^{244}$Cm in the deep region I of cold reaction valley, and the systems $^{62}$Fe + $^{240}$Pu, $^{64}$Fe + $^{238}$Pu, $^{68}$Ni + $^{234}$U, $^{70}$Ni + $^{232}$U, $^{72}$Ni + $^{230}$U, $^{74}$Zn + $^{228}$Th in the other cold valleys are identified as the better projectile-target combinations for the synthesis of $^{302}$120. Our prediction on the synthesis of $^{302}$120 superheavy nuclei using the combinations $^{54}$Cr+$^{248}$Cm, $^{58}$Fe+$^{244}$Pu, $^{64}$Ni+$^{238}$U and $^{50}$Ti+$^{249}$Cf are compared with available experimental data and other theoretical predictions.

Probable Projectile-Target Combinations for the Synthesis of Super Heavy Nucleus 286112

The fusion cross sections for the reactions of all the projectile-target combinations found in the cold valleys of 286 112 have been studied using scattering potential as the sum of Coulomb and proximity potential, so as to predict the most probable projectile-target combinations in heavy ion fusion reactions for the synthesis of super heavy nucleus 286 112. While considering the nature of potential pockets and half lives of the colliding nuclei, the systems 82 Ge + 204 Hg, 80 Ge + 206 Hg and 78 Zn + 208 Pb found in the deep cold valley region and the systems 48 Ca+ 238 U, 38 S+ 248 Cm and 44 Ar+ 242 Pu in the cold valleys are predicted to be the better optimal projectile-target combinations for the synthesis of super heavy nucleus 286 112.

Cold reaction valleys in the radioactive decay of superheavy 286112, 292114, and 296116 nuclei

Cold reaction valleys in the radioactive decay of superheavy nuclei {286}^112, {292}^114 and {296}^116 are studied taking Coulomb and Proximity Potential as the interacting barrier. It is found that in addition to alpha particle, 8^Be, 14^C, 28^Mg, 34^Si, 50^Ca, etc. are optimal cases of cluster radioactivity since they lie in the cold valleys. Two other regions of deep minima centered on 208^Pb and 132^Sn are also found. Within our Coulomb and Proximity Potential Model half-life times and other characteristics such as barrier penetrability, decay constant for clusters ranging from alpha particle to 68^Ni are calculated. The computed alpha half-lives match with the values calculated using Viola--Seaborg--Sobiczewski systematics. The clusters 8^Be and 14^C are found to be most probable for emission with T_1/2 < 1030s. The alpha-decay chains of the three superheavy nuclei are also studied. The computed alpha decay half-lives are compared with the values predicted by Generalized Liquid Drop Model and they are found to match reasonably well.

Systematic study of heavy cluster emission from 210–226Ra isotopes

The half lives for various clusters lying in the cold reaction valleys of {210-226}^Ra isotopes are computed using our Coulomb and proximity potential model (CPPM). The computed half lives of 4^He and 14^C clusters from {210-226}^Ra isotopes are in good agreement with experimental data. Half lives are also computed using the Universal formula for cluster decay (UNIV) of Poenaru et al., and are found to be in agreement with CPPM values. Our study reveals the role of doubly magic 208^Pb daughter in cluster decay process. Geiger - Nuttall plots for all clusters up to 62^Fe are studied and are found to be linear with different slopes and intercepts. {12,14}^C emission from 220^Ra; 14^C emission from {222,224}^Ra; 14^C and 20^O emission from 226^Ra are found to be most favourable for measurement and this observation will serve as a guide to the future experiments.

Systematic decay studies of even–even 132–138Nd, 144–158Gd, 176–196Hg and 192–198Pb isotopes

The alpha and cluster decay properties of the 132–138Nd, 144–158Gd, 176–196Hg and 192–198Pb even–even isotopes in the two mass regions A = 130 – 158 and A = 180 – 198 are analyzed using the Coulomb and Proximity Potential Model. On examining the clusters at corresponding points in the cold valleys (points with same A 2 ) of the various isotopes of a particular nucleus we find that at certain mass numbers of the parent nuclei, the clusters emitted are getting shifted to the next lower atomic number. It is interesting to see that the change in clusters appears at those isotopes where a change in shape is occurring correspondingly. Such a change of clusters with shape change is studied for the first time in cluster decay. The alpha decay half lives of these nuclei are computed and these are compared with the available experimental alpha decay data. It is seen that the two are in good agreement. On making a comparison of the alpha half lives of the normal deformed and superdeformed nuclei, it can be seen that the normal deformed 132Nd, 176–188Hg and 192Pb nuclei are found to be better alpha emitters than the superdeformed (in excited state) 134,136Nd, 190–196Hg and 194Pb nuclei. The cluster decay studies reveal that as the atomic number of the parent nuclei increases the N ≠ Z cluster emissions become equally or more probable than the N = Z emissions. On the whole the alpha and cluster emissions are more probable from the parents in the heavier mass region ( A = 180 – 198 ) than from the parents in the lighter mass region ( A = 130 – 158 ). The effect of quadrupole ( β 2 ) and hexadecapole ( β 4 ) deformations of parent and fragments on half life times are also studied.

Microscopic cold fission yields ofCf252

We show that the sharp maximum corresponding to $^{107}\mathrm{Mo}$ in the fragment distribution of the $^{252}\mathrm{Cf}$ cold fission is actually a Sn-like radioactivity, similar to other decay processes in which magic nuclei are involved, namely $\ensuremath{\alpha}$ decay and heavy cluster emission, also called Pb-like radioactivity. It turns out that the mass asymmetry degree of freedom has a key role in connecting initial Sn with the final Mo isotopes along the fission path. We investigate the cold rearrangement of nucleons within the framework of the two-center shell model in order to compute the cold valleys in the charge equilibrated fragmentation potential. The fission yields are estimated by using the semiclassical penetration approach. We consider 5 degrees of freedom, namely the interfragment distance, the shapes of fragments, the neck parameter, and mass asymmetry. We found an isomeric minimum between the internal and external barriers. It turns out that the inner cold valley of the total potential energy is connected to the doubly magic isotope $^{132}\mathrm{Sn}$.

Isotopic evidence for the provenance and turnover of organic carbon by soil microorganisms in the Antarctic dry valleys

The extremely cold and arid Antarctic dry valleys are one of the most environmentally harsh terrestrial ecosystems supporting organisms in which the biogeochemical transformations of carbon are exclusively driven by microorganisms. The natural abundance of (13)C and (15)N in source organic materials and soils have been examined to obtain evidence for the provenance of the soil organic matter and the C loss as CO(2) during extended incubation (approximately 1200 days at 10 degrees C under moist conditions) has been used to determine the potential decay of soil organic C. The organic matter in soils remote from sources of liquid water or where lacustrine productivity was low had isotope signatures characteristic of endolithic (lichen) sources, whereas at more sheltered and productive sites, the organic matter in the soils that was a mixture mainly lacustrine detritus and moss-derived organic matter. Soil organic C declined by up to 42% during extended incubation under laboratory conditions (equivalent to 50-73 years in the field on a thermal time basis), indicating relatively fast turnover, consistent with previous studies indicating mean residence times for soil organic C in dry valley soils in the range 52-123 years and also with recent inputs of relatively labile source materials.

Slowest to fastest: Extreme range in lichen growth rates supports their use as an indicator of climate change in Antarctica

Global temperature rise is suggested to be greater and more rapid in polar regions. There has been a clear temperature rise of 0.056 °C y −1 in the Antarctic Peninsula and this has led to changes in higher plant extent and range. In the more extreme environments of the main continent the vegetation is scattered and composed of lichens and mosses. There is interest in the possible effects of global climate change on these communities acting through changes in temperature and precipitation. Lichens have been extensively used to date the substrates on which they are growing using the techniques of lichenometry. The slow growth and longevity of lichens particularly suites them for this use. We present evidence that there appears to be a substantial (two orders of magnitude) cline in lichen growth rate from the warmer, wetter and more productive Peninsula to the cold Dry Valleys at 77°S latitude. The differences in growth rate reflect the precipitation and temperature regimes at the different sites. The large range in growth rates coupled with the simplicity of measuring lichen growth using modern techniques suggests that this could be an excellent tool for the detection of climate change in continental Antarctica.

Fusion hindrance and roles of shell effects in superheavy mass region

We present the first attempt of systematically investigating the effects of shell correction energy for a dynamical process, which includes fusion, fusion–fission and quasi-fission processes. In the superheavy mass region, for the fusion process, shell correction energy plays a very important role and enhances the fusion probability when the colliding partner has a strong shell structure. By analyzing the trajectory in three-dimensional coordinate space with the Langevin equation, we reveal the mechanism of the enhancement of the fusion probability caused by ‘cold fusion valleys’. The temperature dependence of shell correction energy is considered.

Cold valleys of superheavy elements with deformed targets and projectiles

The dependence of the cold driving potential on the deformation of the incoming target and projectile is investigated in the case of the synthesis of the superheavy nuclei 256No, 286112, 292114, 296116, and 306122. The occurrence of valleys in the driving potential as a function on the interfragment distance and the mass asymmetry is studied for different fixed orientations of the colliding nuclei such as the pole-pole, pole-equator, equator-equator, and equator-equator-crossed and compared to the case when the nuclei are assumed to be spherical or when the potential is averaged over the orientation.

Extension of the periodic system in the sectors of strangeness and antimatter

The extension of the known periodic system into new regions is discussed. One direction is the extrapolation to large mass numbers,i.e. the predicted island of superheavy nuclei. The production mechanism and decay processes of superheavy nuclei through cold valleys are discussed. Other promising new directions are the sectors of hypernuclei and antinuclei. The collective formation of clusters of hypermatter and antimatter in the highly compressed reaction zone of relativistic nucleus-nucleus collsions is considered in the framework of meson-field theory.

Effects of electron-hole scattering on transient transport in p-type silicon

The effects of electron-hole scattering on the transient transport of minority electrons in room-temperature silicon is examined using an ensemble Monte Carte approach. The transport model includes the dynamics of both electrons and holes with coupling between the electron and hole systems through their Coulombic interaction. Calculations are reported for an acceptor concentration of 1018cm-3 with applied electric field strengths of 10 and 29 kV cm-1. The calculations show that electron-hole scattering reduces mobility, velocity overshoot and energy in both hot and cold valleys, and that the valley repopulation rate is reduced for an applied field of 10 kV cm-1 while at 20 kV cm-1 it is enhanced at times longer than one picosecond.

Monte Carlo investigation of minority electron transport in silicon

The transport of minority electrons in silicon has been investigated using an ensemble Monte Carlo approach at room temperature with electron-hole scattering rates which take into account the ellipsoidal nature of the conduction band valleys. Mobility calculations showed quantitative agreement with experimental values at an acceptor concentration of 4.5×1016 cm−3 while qualitative agreement with the electron-hole drag effect was observed at 3.8×1018 cm−3. Transient calculations showed the electron-hole interactions decrease electron energy, reduce steady-state velocity, and decrease the transfer rate of electrons to the cold valleys.

Carrier-carrier interaction effects on transient valley repopulation and velocity in silicon

The effects of carrier-carrier interactions on the transient valley repopulation and velocity in bulk silicon has been investigated using an ensemble Monte Carlo method. The expressions for electron-electron scattering rates take into account the ellipsoidal nature of the energy surfaces in silicon. The relative effects of both electron-plasmon and short range e-e interactions strongly depend on the orientation and magnitude of the electric fields. The e-e interactions reduce the transfer rates of electrons from the hot valleys to the cold valleys, increase the energy of the electrons in the cold valleys, and reduce the transient velocity overshoot in the hot valleys. These effects are more significant at higher electron concentration.