Evaporation of ices near massive stars: models based on laboratory TPD data

Hot cores and their precursors contain an integrated record of the physics of the collapse process in the chemistry of the ices deposited during that collapse. In this paper, we present results from a new model of the chemistry near high mass stars in which the desorption of each species in the ice mixture is described as indicated by new experimental results obtained under conditions similar to those hot cores. Our models show that provided there is a monotonic increase in the temperature of the gas and dust surrounding the protostar, the changes in the chemical evolution of each species due to differential desorption are important. The species H$_2$S, SO, SO$_2$, OCS, H$_2$CS, CS, NS, CH$_3$OH, HCOOCH$_3$, CH$_2$CO, C$_2$H$_5$OH show a strong time dependence that may be a useful signature of time evolution in the warm-up phase as the star moves on to the Main Sequence. This preliminary study demonstrates the consequences of incorporating reliable TPD data into chemical models.Comment: 5 pages, accepted by MNRA

Rapid evolution of protein kinase PKR alters sensitivity to viral inhibitors.

Protein kinase PKR (also known as EIF2AK2) is activated during viral infection and phosphorylates the alpha subunit of eukaryotic translation initiation factor 2 (eIF2), leading to inhibition of translation and viral replication. We report fast evolution of the PKR kinase domain in vertebrates, coupled with positive selection of specific sites. Substitution of positively selected residues in human PKR with residues found in related species altered sensitivity to PKR inhibitors from different poxviruses. Species-specific differences in sensitivity to poxviral pseudosubstrate inhibitors were identified between human and mouse PKR, and these differences were traced to positively selected residues near the eIF2alpha binding site. Our findings indicate how an antiviral protein evolved to evade viral inhibition while maintaining its primary function. Moreover, the identified species-specific differences in the susceptibility to viral inhibitors have important implications for studying human infections in nonhuman model systems

Evaluation of thermal control coatings for use on solar dynamic radiators in low Earth orbit

Thermal control coatings with high thermal emittance and low solar absorptance are needed for Space Station Freedom (SSF) solar dynamic power module radiator (SDR) surfaces for efficient heat rejection. Additionally, these coatings must be durable to low earth orbital (LEO) environmental effects of atomic oxygen, ultraviolet radiation and deep thermal cycles which occur as a result of start-up and shut-down of the solar dynamic power system. Eleven candidate coatings were characterized for their solar absorptance and emittance before and after exposure to ultraviolet (UV) radiation (200 to 400 nm), vacuum UV (VUV) radiation (100 to 200 nm) and atomic oxygen. Results indicated that the most durable and best performing coatings were white paint thermal control coatings Z-93, zinc oxide pigment in potassium silicate binder, and YB-71, zinc orthotitanate pigment in potassium silicate binder. Optical micrographs of these materials exposed to the individual environmental effects of atomic oxygen and vacuum thermal cycling showed that no surface cracking occurred

Perfect State Transfer in Laplacian Quantum Walk

For a graph $G$ and a related symmetric matrix $M$, the continuous-time quantum walk on $G$ relative to $M$ is defined as the unitary matrix $U(t) = \exp(-itM)$, where $t$ varies over the reals. Perfect state transfer occurs between vertices $u$ and $v$ at time $\tau$ if the $(u,v)$-entry of $U(\tau)$ has unit magnitude. This paper studies quantum walks relative to graph Laplacians. Some main observations include the following closure properties for perfect state transfer: (1) If a $n$-vertex graph has perfect state transfer at time $\tau$ relative to the Laplacian, then so does its complement if $n\tau$ is an integer multiple of $2\pi$. As a corollary, the double cone over any $m$-vertex graph has perfect state transfer relative to the Laplacian if and only if $m \equiv 2 \pmod{4}$. This was previously known for a double cone over a clique (S. Bose, A. Casaccino, S. Mancini, S. Severini, Int. J. Quant. Inf., 7:11, 2009). (2) If a graph $G$ has perfect state transfer at time $\tau$ relative to the normalized Laplacian, then so does the weak product $G \times H$ if for any normalized Laplacian eigenvalues $\lambda$ of $G$ and $\mu$ of $H$, we have $\mu(\lambda-1)\tau$ is an integer multiple of $2\pi$. As a corollary, a weak product of $P_{3}$ with an even clique or an odd cube has perfect state transfer relative to the normalized Laplacian. It was known earlier that a weak product of a circulant with odd integer eigenvalues and an even cube or a Cartesian power of $P_{3}$ has perfect state transfer relative to the adjacency matrix. As for negative results, no path with four vertices or more has antipodal perfect state transfer relative to the normalized Laplacian. This almost matches the state of affairs under the adjacency matrix (C. Godsil, Discrete Math., 312:1, 2011).Comment: 26 pages, 5 figures, 1 tabl

Impact des terrils houillers sur la qualité des eaux souterraines (bassin minier Nord-Pas-de-Calais, France) : approche géochimique et isotopique

L'exploitation du charbon dans le Nord-Pas-de-Calais (France) a engendré le dépôt d'importantes quantités de résidus miniers sous forme de terrils, essentiellement constitués de schistes houillers. Le lessivage de ces stériles par les eaux météoriques et l'oxydation des sulfures de fer contenus sont susceptibles de contribuer à l'enrichissement en sulfates et métaux associés de l'aquifère de la craie, principale ressource en eau de la région. Des analyses chimiques et isotopiques (S & C) ont été effectuées sur des prélèvements d'eau en amont et en aval hydraulique des sites d'étude ainsi que sur la fraction minérale des terrils. Afin de déterminer les modalités d'infiltration des eaux météoriques au sein des terrils, des prospections radio-magnétotelluriques, couplées à des mesures de perméabilité et de granularité ont été effectuées. Les analyses ont permis de mettre en évidence que le lessivage des terrils entraîne un flux d'ions sulfate et de carbone vers l'aquifère de la craie. L'approche géophysique a permis de mettre en évidence un phénomène d'infiltration des eaux météoriques. Elle a montré en outre l'existence de barrières de perméabilité en profondeur. Il apparaît donc que les eaux météoriques, lorsqu'elles s'infiltrent dans le terril, ne peuvent pénétrer à plus de quelques mètres de profondeur. L'existence de zones imperméables, en limitant l'infiltration des eaux en profondeur, limite également la quantité de sulfure potentiellement oxydable et donc la quantité de sulfates entraînée vers l'aquifère de la craie.In the Nord-Pas-de-Calais region (France), coal mining activity has induced a build-up of many mine tips. The tip materials are dominantly composed of siltstones, locally rich in iron sulfide. Weathering of pyrite might be expected to release sulfate ions and associated metals within the run-off waters down to the underlying aquifer, which is composed of a thick Cretaceous chalk formation. The objectives of this study were twofold: (1) to determine the possible role of the mine tips in the sulfate mineralization of the chalk aquifer and; (2) to assess the amount of waste material that can be leached and may supply sulfate ions to the water table.Two sites were selected for this study. Site 1 rests directly on the Senonian-Turonian chalk, whereas site 2 lies on sandy-clayey Cenozoic formations overlying the chalk formations (Figs. 1-2). Water samples were collected within the chalk aquifer (Fig. 3), which represents a free water table except for where the almost impermeable Cenozoic formations confine this table (site 2). Rock samples were collected at the surface and at a depth of <12 m at both sites. Various analyses were performed on these samples including mineralogical analyses carried out on both the bulk fraction and the clayey fraction, as well as elementary analyses of total carbon, total sulfur and CaCO3 contents. Elemental analyses were carried out by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES: major and minor elements) or Inductively Coupled Plasma-Mass Spectrometry (ICP-MS: trace elements). Chemical and isotopic (C, S) analyses were performed on water sampled from upstream and downstream of the mine tips. In situ measurements were also carried out during sampling. Finally, to assess the degree of rainwater seeping through the coal mine tips, two radio-magnetotelluric surveys were carried out in September and November, 1999 following rainy periods. Permeability measurements and grain-size analyses of subsurface samples were also performed at site 2.The carbon and sulfur contents showed superficial leaching on the mine tips (Fig. 4). The use of sulfur isotopes as tracers of the sulfate origin allowed identification of two sources for the two sites: a "mine tip" source with a slightly negative d34 S (-2.8‰ to -3.9‰), which corresponds to the oxidation of sulfides contained by the Carboniferous shales, and another source (d34 S=-20‰) corresponding to the gypsum of the Cenozoic formations, which was only present at site 2 (Figs. 5 & 6).This study outlined different behavior for the tips of the two sites. At site 1, where there is a free water-table zone, the mine tip leachates carry sulfate ions directly to the water table, whereas in the case of a confined aquifer zone such as the one present at site 2, a proportion of the sulfate was reduced once exported to the water table (the redox potential showed negative values; Table 1). This suggestion of bacterially-mediated reduction is supported by the d34 S of the sulfate content in the water table. The bacterial activity was fueled by the organic carbon release that accompanies the sulfur leaching on the mine tips. This carbon contribution was confirmed by the 14C activity that characterized the chalk aquifer waters at the upstream region of the mine tip and noticeably decreased downstream. The decrease is a result of the supply of "dead carbon" from the mine tips (Fig. 7).The oxidation of pyrite also results in H+ production. However, the pH decrease observed downstream from the sites was very slight. Waters derived from leaching of the mine tip seeped through the buffered environment of the chalk aquifer. The distribution of metal content showed no surface to depth gradient for samples taken from both sites. The only evidence of "neutral acid mining drainage" (NAMD) was the sulfate amounts exported, and the increase in Mg, Ca, HCO3- and Sr contents observed downstream from the sites (Table 2a-b).The decrease in the apparent resistivity of radio-magnetotelluric profiles demonstrated that rain waters could deeply penetrate in some parts of the tip at site 2 (Fig. 9). Considering the constant nature of the waste material (grain size and porosity), a decrease in resistivity accompanied by an increase in conductivity between the two surveys indicated water seepage. Permeability measurements showed the occurrence of deep permeability barriers (Fig. 10), limiting not only rainwater seepage, but also the amount of mobilizable sulfide and consequently the amount of sulfates exported to the chalk aquifer. Grain size is not the only reason for the permeable or impermeable nature of waste material - the grain ordering and the compaction of levels at depth also have a role

Low-Silica and High-Calcium Stone in the Newman Limestone (Mississippian) on Pine Mountain, Harlan County, Southeastern Kentucky

The coal industry of Kentucky is an important market for limestone. Coal producers use limestone as rock dust for explosion abatement in underground coal mines and as a neutralizing agent in surface-mine reclamation and acid-drainage control. Crushed stone is also used for constructing and maintaining haulage roads. In the Eastern Kentucky Coal Field, the coal-bearing rocks of Pennsylvanian age generally do not contain limestones that are thick enough to quarry or mine economically. But movement on the Pine Mountain overthrust fault has brought the Newman Limestone (Mississippian) to the surface along Pine Mountain in the southeastern part of the coal field. The Newman on Pine Mountain in Harlan County was sampled at 1-foot intervals to determine its chemical quality and potential for industrial use, particular as low-silica rock dust. The sampled section contains two zones of low-silica stone, 64 and 25 feet thick, averaging 0.82 and 1.01 percent silica (SiO2), respectively. Intervals of high-calcium limestone are present in the low-silica zones. These deposits are potentially suitable for use as rock dust in underground coal mines and as neutralizing agents in surface-mine reclamation and acid-drainage control. The intervals of chemically pure stone in Harlan County may be sufficiently thick to produce by selective quarrying or underground mining. Exploitation of the Newman deposits, however, will be complicated by the steep southeastward to southward dip (13 to 42°) of the beds, displacement along small faults within the limestone, and fracturing

Heat and salt balances over the northern California shelf in winter and spring

Heat and salt balances are estimated over the northern California shelf from early December 1988 through late February 1989 (winter) and from early March through early May 1989 (spring) from moored meteorological and oceanographic time series taken in 93 m of water 6.3 km from the coast. We find a winter mean offshore heat flux of 8.7 x 10⁵ W m¯¹, about a factor of 5 smaller than earlier estimates of the mean summer (upwelling season) offshore heat flux on the northern California shelf. The mean offshore heat flux is predominantly in the surface boundary layer and is balanced by an along-shelf heat flux divergence (as represented by an eddy along-shelf temperature gradient flux) and a cooling trend making the mean winter heat balance fundamentally three dimensional. In contrast to winter, the spring mean offshore heat flux of 6.4 x l0⁵ W m¯¹ is balanced by a positive air-sea heat flux of 8.3 x 10⁵ W m¯¹ which is about 80% of the mean air-sea heat flux in summer. This makes the spring mean heat budget primarily two dimensional, like the summer mean heat budget off northern California. On timescales of days the dominant terms in the fluctuating heat budget in both winter and spring are the cross-shelf heat flux and local changes in heat content. These are well correlated with each other and with the local along-shelf wind stress. The along-shelf temperature gradient flux, uncorrelated with the along-shelf wind stress, is usually weak on timescales of days. Occurrences when it is strong are interpreted as effects of mesoscale features. Mean and fluctuating cross-shelf salt fluxes provide essentially the same information as cross-shelf heat fluxes. This is not surprising in light of the strong temperature-salinity relationship on the northern California shelf

Double-stranded RNA-activated protein kinase PKR of fishes and amphibians: Varying the number of double-stranded RNA binding domains and lineage-specific duplications

BackgroundDouble-stranded (ds) RNA, generated during viral infection, binds and activates the mammalian anti-viral protein kinase PKR, which phosphorylates the translation initiation factor eIF2alpha leading to the general inhibition of protein synthesis. Although PKR-like activity has been described in fish cells, the responsible enzymes eluded molecular characterization until the recent discovery of goldfish and zebrafish PKZ, which contain Z-DNA-binding domains instead of dsRNA-binding domains (dsRBDs). Fish and amphibian PKR genes have not been described so far.ResultsHere we report the cloning and identification of 13 PKR genes from 8 teleost fish and amphibian species, including zebrafish, demonstrating the coexistence of PKR and PKZ in this latter species. Analyses of their genomic organization revealed up to three tandemly arrayed PKR genes, which are arranged in head-to-tail orientation. At least five duplications occurred independently in fish and amphibian lineages. Phylogenetic analyses reveal that the kinase domains of fish PKR genes are more closely related to those of fish PKZ than to the PKR kinase domains of other vertebrate species. The duplication leading to fish PKR and PKZ genes occurred early during teleost fish evolution after the divergence of the tetrapod lineage. While two dsRBDs are found in mammalian and amphibian PKR, one, two or three dsRBDs are present in fish PKR. In zebrafish, both PKR and PKZ were strongly upregulated after immunostimulation with some tissue-specific expression differences. Using genetic and biochemical assays we demonstrate that both zebrafish PKR and PKZ can phosphorylate eIF2alpha in yeast.ConclusionConsidering the important role for PKR in host defense against viruses, the independent duplication and fixation of PKR genes in different lineages probably provided selective advantages by leading to the recognition of an extended spectrum of viral nucleic acid structures, including both dsRNA and Z-DNA/RNA, and perhaps by altering sensitivity to viral PKR inhibitors. Further implications of our findings for the evolution of the PKR family and for studying PKR/PKZ interactions with viral gene products and their roles in viral infections are discussed

PNAS plus: plasmodium falciparum responds to amino acid starvation by entering into a hibernatory state

The human malaria parasite Plasmodium falciparum is auxotrophic for most amino acids. Its amino acid needs are met largely through the degradation of host erythrocyte hemoglobin; however the parasite must acquire isoleucine exogenously, because this amino acid is not present in adult human hemoglobin. We report that when isoleucine is withdrawn from the culture medium of intraerythrocytic P. falciparum, the parasite slows its metabolism and progresses through its developmental cycle at a reduced rate. Isoleucine-starved parasites remain viable for 72 h and resume rapid growth upon resupplementation. Protein degradation during starvation is important for maintenance of this hibernatory state. Microarray analysis of starved parasites revealed a 60% decrease in the rate of progression through the normal transcriptional program but no other apparent stress response. Plasmodium parasites do not possess a TOR nutrient-sensing pathway and have only a rudimentary amino acid starvation-sensing eukaryotic initiation factor 2α (eIF2α) stress response. Isoleucine deprivation results in GCN2-mediated phosphorylation of eIF2α, but kinase-knockout clones still are able to hibernate and recover, indicating that this pathway does not directly promote survival during isoleucine starvation. We conclude that P. falciparum, in the absence of canonical eukaryotic nutrient stress-response pathways, can cope with an inconsistent bloodstream amino acid supply by hibernating and waiting for more nutrient to be provided

Low-Silica and High-Calcium Stone in the Newman Limestone (Mississippian) on Pine Mountain, Letcher County, Southeastern Kentucky

The coal industry of Kentucky is an important market for limestone. Coal producers use limestone as rock dust for explosion abatement in underground coal mines and as a neutralizing agent in surface-mine reclamation and acid-drainage control. Haulage-road construction and maintenance require crushed stone. Coal-bearing rocks of Pennsylvanian age in the Eastern Kentucky Coal Field generally do not contain limestones that are sufficiently thick to quarry or mine economically, but in the southeastern part of the coal field, fault movement has brought the Newman Limestone to the surface along Pine Mountain. The Newman was sampled at three sites in Letcher County to determine its chemical quality and potential for industrial use, particularly as a source of low-silica rock dust. Analysis of the foot-by-foot samples shows that the Newman contains several zones of low-silica stone, 10 to 39 feet thick. A few intervals of high-calcium limestone, 12 to 24 feet thick, coincide with or occur in the low-silica zones. The deposits of low-silica and high-calcium stone are thickest in the southwestern part of Letcher County and commonly thin northeastward. The thicker deposits of chemically pure limestone and dolomite may be an economically exploitable source of rock dust for underground coal mines, and a source of stone for surface-mine reclamation and acid-drainage control. Production from deposits in the Newman, however, will be complicated by the steep southeastward to southward dip (20 to 42°) of the beds, possible displacement along small faults, and fracturing of the limestone