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The focus of this work is on two topics: (i) formation of complex organic molecules (COMs) and (ii) isotope fractionation. Various COMs, which are C, H-containing molecules consisting of 6 atoms and more, have been detected in the central warm region of protostellar cores. Most of this review is about gas-grain chemical models, which have been constructed to evaluate the mechanisms and efficiency of the COM formation. The relevant physical and chemical processes are investigated in laboratory experiments, as reported in other articles in this volume.
The isotope fractionation of volatile elements is observed in both the interstellar medium (ISM) and Solar system material. While exothermic exchange reactions enrich molecules with heavier isotopes such as Deuterium, the isotope selective photodissociation can be coupled with ice formation to enrich the ice mantle with rare isotopes. The efficiency of this fractionation depends on the photodesorption yields, which has been studied in laboratory experiments.
Wernicke encephalopathy (WE) is a neuropsychiatric disorder caused by thiamine deficiency, and is sometimes overlooked because of the diversity of clinical symptoms.
From a series of WE patients with cancer, we report a lung cancer patient who developed WE, the main symptom of which was agitation.
A 50-year-old woman with lung cancer was referred to our psycho-oncology clinic because of agitation lasting for three days. No laboratory findings or drugs explaining her agitation were identified. Although the patient did not develop delirium, ophthalmoplegia, or ataxia, WE was suspected because she experienced a loss of appetite loss lasting 5 weeks. This diagnosis was supported by abnormal serum thiamine and disappearance of agitation one hour after intravenous thiamine administration.
Significance of results
This report emphasizes the clinical diversity of WE and indicates the limits of the ability to diagnose WE from typical clinical symptoms. The presence of a loss of appetite for more than two weeks may be the key to the accurate diagnosis of WE.
Thiamine is an essential coenzyme for oxidative metabolisms; however, it is not synthesized in the human body, and the average thiamine storage capacity is approximately 18 days. Therefore, thiamine deficiency (TD) can occur in any condition of unbalanced nutrition. If TD is left untreated, it causes the neuropsychiatric disorder Wernicke encephalopathy (WE). Although WE is a medical emergency, it is sometimes overlooked because most patients with WE do not exhibit all of the typical symptoms, including delirium, ataxia, and ophthalmoplegia. If all of the typical clinical symptoms of WE are absent, diagnosis of TD or WE becomes more difficult.
From a series of cancer patients, we reported three patients who developed TD without the typical clinical symptoms of WE.
A 69-year-old woman with pancreatic body cancer receiving chemotherapy with paclitaxel and gemcitabine for six months. Her performance status (PS) was 1. A detailed interview revealed that she had appetite loss for six months. Another 69-year-old woman with ovarian cancer received nedaplatin; her PS was 0. A detailed interview revealed that she had appetite loss for three months. A 67-year-old woman with colon cancer receiving ramucirumab in combination with second-line fluorouracil with folinic acid and irinotecan. Her PS was 1. A detailed interview revealed that she had appetite loss for three weeks. None exhibited typical clinical signs of WE, but they developed appetite loss for six months, three months, and three weeks, respectively. The diagnosis of TD was supported by abnormally low serum thiamine levels.
Significance of the results
This report emphasizes the possibility of TD in cancer patients even when patients do not develop typical clinical signs of WE. The presence of appetite loss for more than two weeks may aid in diagnosing TD. Patients receiving chemotherapy may be at greater risk for developing TD.
Wernicke encephalopathy (WE) is a neuropsychiatric disorder caused by thiamine deficiency. Several reports of WE in cancer patients are known. WE is sometimes overlooked because most patients do not exhibit its typical symptoms (e.g., delirium, ataxia, ocular palsy). If delirium is not present, a diagnosis of WE is difficult because delirium is the hallmark symptom of WE.
Taken from a series on WE in cancer, we report two patients who developed WE without delirium during periodic psycho-oncology outpatient visits.
Case 1. A 61-year-old woman with non-Hodgkin lymphoma who was periodically attending a psycho-oncology outpatient clinic developed an unsteady gait. WE was suspected because she also developed appetite loss for two weeks, and we could find no other laboratory findings to explain her unsteady gait. Our diagnosis was supported by abnormal serum thiamine and disappearance of the gait disturbance after intravenous thiamine administration. Case 2. A 50-year-old woman with breast carcinoma with bone metastasis developed an unsteady gait. WE was suspected because she also developed loss of appetite for two weeks, and no other laboratory findings could explain her unsteady gait. The diagnosis was supported by abnormal serum thiamine and disappearance of the gait disturbance after administration of intravenous thiamine.
Significance of Results:
Our report emphasizes the importance of being aware of WE, even when patients do not present with delirium. The presence of loss of appetite for more than two weeks may be the key to a diagnosis of WE.
The level of isotopic fractionation in molecules provides insights into their formation environments and how they formed. In this article, we review hydrogen and nitrogen isotopic fractionation in low-mass star-forming regions. Interstellar molecules are significantly enriched in deuterium. The importance of the nuclear spin states of light species on deuterium fractionation and the usefulness of singly and doubly deuterated molecules as chemical tracers are discussed. Observations have revealed that molecules in prestellar cores are enriched in or depleted in 15N depending on molecules. Compared with deuterium fractionation chemistry, our understanding of 15N fractionation chemistry is not well established. We briefly discuss potential 15N fractionation routes, i.e., isotopic-exchange reactions and isotopic selective photodissociation of N2. In addition, the selective freeze-out of 15N atoms onto dust grains around the transition between N atoms and N2 is discussed as a potential mechanism that causes the depletion of 15N in the gas phase.
Molecular oxygen, O2, was recently detected in comet 67P by the ROSINA instrument on board the Rosetta spacecraft with a surprisingly high abundance of 4% relative to H2O, making O2 the fourth most abundant in comet 67P. Other volatile species with similar volatility, such as molecular nitrogen N2, were also detected by Rosetta, but with much lower abundances and much weaker correlations with water. Here, we investigate the chemical and physical origin of O2 and other volatile species using the new constraints provided by Rosetta. We follow the chemical evolution during star formation with state-of-the-art astrochemical models applied to dynamical physical models by considering three origins: i) in dark clouds, ii) during forming protostellar disks, and iii) during luminosity outbursts in disks. The models presented here favour a dark cloud (or “primordial”) grain surface chemistry origin for volatile species in comets, albeit for dark clouds which are slightly warmer and denser than those usually considered as solar system progenitors.
We investigate the molecular evolution in star forming cores from dense cloud cores (nH ~ 104 cm−3, T ~ 10 K) to protostellar cores. A detailed gas-grain reaction network is solved in infalling fluid parcels in 1-D radiation hydrodynamic model. Large organic molecules are mainly formed via grain-surface reaction at T ~ several 10 K and sublimated to the gas-phase at ~ 100 K, while carbon-chain species are formed at a few 10 K after the sublimation of CH4 ice. The former accounts for the high abundance of large organic molecules in hot corinos such as IRAS16293, and the latter accounts for the carbon chain species observed toward L1527. The relative abundance of carbon chain species and large organic species would depend on the collapse time scale and/or temperature in the dense core stage. The large organic molecules and carbon chains in the protostellar cores are heavily deuterated; although they are formed in the warm temperatures, their ingredients have high D/H ratios, which are set in the cold core phase and isothermal collapse phase. HCOOH is formed by the gas-phase reaction of OH with the sublimated H2CO, and is further enriched in Deuterium due to the exothermic exchange reaction of OH + D → OD + H.
In the fluid parcels of the 1-D collapse model, warm temperature T. ~ several 10 K lasts for only ~ 104 yr, and the fluid parcels fall to the central star in ~ 100 yr after the temperature of the parcel rises to T ≥ 100 K. These timescales are determined by the size of the warm region and infall (~ free-fall) velocity: rwarm/tff. In reality, circum stellar disk is formed, in which fluid parcels stay for a longer timescale than the infall timescale. We investigate the molecular evolution in the disk by simply assuming that a fluid parcel stays at a constant temperature and density (i.e. a fixed disk radius) for 104 − 105 yrs. We found that some organic species which are underestimated in our 1-D collapse model, such as CH3OCH3 and HCOOCH3, become abundant in the disk. We also found that these disk species have very high D/H ratio as well, since their ingredients are highly deuterated.
Finally we investigate molecular evolution in a 3D hydrodynamic simulation of star forming core. We found CH3OH are abundant in the vicinity of the first core. The abundances of large organic species are determined mainly by the local temperature (sublimation), because of the short lifetime of the first core and the efficient mass accretion via angular momentum transfer.
Two kinds of obviously different-sized –Si3N4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si Kβ bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si3N4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si3N4 whiskers were grown from the surface of Si3N4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si3N4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si3N4 single crystals.
In the safety assessment of high level radioactive waste disposal, a significant retardation of nuclides can be expected. When radionuclides released from an underground repository are transported with the moving groundwater along cracks in the rock, the radionuclides will be retarded by not only adsorption on the surface of the cracks but also diffusion into the micropores of rock matrix.
Diffusivities of U(VI) were measured in water-saturated granite that was mined in the middle of Japan. The measured penetration profile of U(VI) was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in granite. One diffusion path was possibly a fissure with a width of a few microns and another was a network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for U(VI) were 10−13-10−12 m2/s through the fissure and 10−15 m2/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This ratio calculated suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.
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