Measurement of thermal conductivity in proton irradiated silicon Khafizov, Marat; Yablinsky, Clarissa; Allen, Todd R. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
04/2014, Letnik:
325
Journal Article
Recenzirano
We investigate the influence of proton irradiation on thermal conductivity in single crystal silicon. We apply a laser based modulated thermoreflectance technique to measure the change in ...conductivity of the thin layer damaged by proton irradiation. Unlike time domain thermoreflectance techniques that require application of a metal film, we perform our spatial domain measurement on uncoated samples. This provides greater sensitivity to the change in conductivity of the thin damaged layer. Using sample temperature as a parameter provides a means to deduce the primary defect structures that limit thermal transport. We find that under high temperature irradiation the degradation of thermal conductivity is caused primarily by extended defects.
Fuel–Cladding Chemical Interactions (FCCIs) in a nuclear reactor occurs due to thermal and radiation enhanced inter-diffusion between the cladding and fuel materials. This can have the detrimental ...effects of reducing the effective cladding wall thickness and the formation of low melting point eutectic compounds. Deposition of thin diffusion barrier coatings in the inner surface of the cladding can potentially reduce or delay the onset of FCCI. This study examines the feasibility of using nanofluid-based electrophoretic deposition (EPD) process to deposit coatings of Yttrium Stabilized Zirconia (YSZ) as the diffusion barrier coating. The deposition parameters, including the nanofluid solvent, additive, particle size, current, and voltage were optimized using test flat substrates of T91 ferritic–martensitic steel. A post deposition sintering step was also conducted and optimized to improve the bonding and mechanical integrity of the coating. Diffusion characteristics of the coatings were investigated by diffusion couple experiments using cerium as a fuel fission product responsible for solid state FCCI. These diffusion couple studies performed at 575°C for 100h showed that the YSZ coatings significantly reduced the solid state inter-diffusion between cerium and steel. A heat transfer model was developed to simulate the changes in temperature profile inside the fuel cladding by addition of YSZ coating. It was found that even though the temperature can increase in the coated cladding, the temperature falls below the melting point of uranium and eutectic temperature in Fe–U phase diagram. Using a co-axial configuration in conjunction with the EPD process, YSZ was successfully deposited uniformly on the inner surfaces of 12″ length sections of cladding with 4mm inner diameter. Such a coating is extremely hard to make by conventional coating technologies like thermal spray or vapor deposition.
Previous research has demonstrated increased stiffness in the multifidus muscle compared to other paraspinal muscles at the fiber bundle level. We aimed to compare single fiber and fiber bundle ...passive mechanical properties of multifidus muscle: (1) in 40 patients undergoing primary versus revision surgery and (2) in muscle with mild versus severe fatty infiltration.
The degree of muscle fatty infiltration was graded using the patients' spine magnetic resonance images. Average single fiber and fiber bundle passive mechanical properties across three tests were compared between primary (
= 30) and revision (
= 10) surgery status, between mild and severe fatty infiltration levels, between sexes, and with age from passive stress-strain tests of excised multifidus muscle intraoperative biopsies.
At the single fiber level, elastic modulus was unaffected by degree of fatty infiltration or surgery status. Female sex (
= 0.001) and younger age (
= 0.04) were associated with lower multifidus fiber elastic modulus. At the fiber bundle level, which includes connective tissue around fibers, severe fatty infiltration (
= 0.01) and younger age (
= 0.06) were associated with lower elastic modulus. Primary surgery also demonstrated a moderate, but non-significant effect for lower elastic modulus (
= 0.10).
Our results demonstrate that female sex is the primary driver for reduced single fiber elastic modulus of the multifidus, while severity of fatty infiltration is the primary driver for reduced elastic modulus at the level of the fiber bundle in individuals with lumbar spine pathology.
14YWT oxide dispersion strengthened (ODS) ferritic steel was irradiated with of 5 MeV Ni super(2+) ions, at 300 degreesC, 450 degreesC, and 600 degreesC to a damage level of 100 dpa. The stability of ...Ti-Y-O nanoclusters was investigated by applying atom probe tomography (APT) in voltage mode, of the samples before and after irradiations. The average size and number density of the nanoclusters was determined using the maximum separation method. These techniques allowed for the imaging of nanoclusters to sizes well below the resolution limit of conventional transmission electron microscopy techniques. The most significant changes were observed for samples irradiated at 300 degreesC where the size (average Guinier radius) and number density of nanoclusters were observed to decrease from 1.1 nm to 0.8 nm and 12 x 10 super(23) to 3.6 x 10 super(23), respectively. In this study, the nanoclusters are more stable at higher temperature.
BackgroundFresh osteochondral allograft transplantation is a well-established technique for the treatment of cartilage defects of the knee. It is believed that the basic paradigm of the technique is ...that the transplantation of viable chondrocytes maintains the articular cartilage matrix over time. Allograft tissue is typically transplanted up to forty-two days after the death of the donor, but it is unknown how the conditions and duration of storage affect the properties of fresh human osteochondral allografts. This study examined the quality of human allograft cartilage as a function of storage for a duration of one, seven, fourteen, and twenty-eight days. We hypothesized that chondrocyte viability, chondrocyte metabolic activity, and the biochemical and biomechanical properties of articular cartilage would remain unchanged after storage for twenty-eight days.MethodsSixty osteochondral plugs were harvested from ten fresh human femoral condyles within forty-eight hours after the death of the donor and were stored in culture medium at 4°C. At one, seven, fourteen, and twenty-eight days after harvest, the osteochondral plugs were analyzed for (1) viability and viable cell density by confocal microscopy, (2) proteoglycan synthesis by quantification of SO4 incorporation, (3) glycosaminoglycan content, (4) indentation stiffness, (5) compressive modulus and hydraulic permeability by static and dynamic compression testing, and (6) tensile modulus by equilibrium tensile testing.ResultsChondrocyte viability and viable cell density remained unchanged after storage for seven and fourteen days (p > 0.7) and then declined at twenty-eight days (p < 0.001). Proteoglycan synthesis remained unchanged at seven days (p > 0.1) and then declined at fourteen days (p < 0.01) and twenty-eight days (p < 0.001). No significant differences were detected in glycosaminoglycan content (p > 0.8), indentation stiffness (p > 0.4), compressive modulus (p > 0.05), permeability (p > 0.3), or equilibrium tensile modulus after storage for twenty-eight days (p > 0.9).ConclusionsThese data demonstrate that fresh human osteochondral allograft tissue stored for more than fourteen days undergoes significant decreases in chondrocyte viability, viable cell density, and metabolic activity, with preservation of glycosaminoglycan content and biomechanical properties. The cartilage matrix is preserved during storage for twenty-eight days, but the chondrocytes necessary to maintain the matrix after transplantation decreased over that time-period.Clinical RelevanceFresh osteochondral allografting is well established and increasingly used, but little information is available about the changes in the tissue that occur during storage over a period of time. Surgeons who perform fresh osteochondral allograft transplantation should understand the consequences of prolonged storage on the quality of the graft.
Ferritic/Martensitic (F/M) steels containing 9 wt.% Cr are candidates for structural and cladding components in the next generation of advanced nuclear fission and fusion reactors. Although it is ...known these alloys exhibit radiation-induced segregation (RIS) at grain boundaries (GBs) while in-service, little is known about the mechanism behind RIS in F/M steels. The classical understanding of RIS in F/M steels presents a mechanism where point defects migrate to GBs acting as perfect sinks. However, variation in grain boundary structure may influence the sink efficiency and these migration processes. A proton irradiated 9 wt.% Cr model alloy steel was investigated using STEM/EDS spectrum imaging and GB misorientation analysis to determine the role of GB structure on RIS at different GBs. An ab initio based rate theory model was developed and compared to the experimental findings. This investigation found Cr preferentially segregates to specific GB structures. The preferential segregation to specific GB structures suggests GB structure plays a key role in the mechanism behind radiation-induced segregation, showing that not all grain boundaries in F/M steels act as perfect sinks. The study also found how irradiation dose and temperature impact the radiation-induced segregation response in F/M steels.
Retrospective case series.
To present results of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in medically nonresponsive pyogenic vertebral osteomyelitis (PVO), treated by ...anterior/posterior debridement and instrumented fusion in the cervical, thoracic, and lumbosacral spine.
Surgical options for PVO vary, as do their outcomes, and can be complicated by recurrence, pseudarthrosis, and death. Although rhBMP-2 use in spinal fusion is increasing, its utility in PVO is unknown. Additionally, use in areas of infection is listed as a contraindication, although this is not supported by laboratory (animal) studies or clinical studies in long bones.
Between 2003 and 2005, 14 patients who underwent circumferential fusion for PVO were included in this study. Average patient age was 54 years (range, 27-77 years). Eight (57%) patients had 3 or more vertebral bodies involved. Diagnostic studies included radiographs, CT, MRI, and markers of infection (C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), white blood count (WBC). All patients underwent anterior fusion with rhBMP-2 inserted in structural allograft (11 patients) or titanium cylindrical cages (3 patients), followed by posterior instrumented fusion with autogenous iliac crest graft (8 occurring on the same day). Follow-up averaged 22 months (range, 11-30 months). All were studied with plain radiographs, including flexion-extension lateral films and fine cut CT scans with reconstruction. Pain ratings were recorded by visual analog scores (VAS).
Clinical resolution of infections, normalization of lab values, and bony fusion, based on dynamic radiographs and CT scans, were seen in all patients at latest follow-up. Staphylococcus aureus was the most frequently identified organism (8 patients). Four (29%) patients had positive blood cultures (all MRSA). Predisposing comorbidities were present in 12 patients. Six patients had epidural abscesses. Eight (57%) patients presented with neurologic deficits, ranging from paraparesis to quadriplegia. Complete recovery was seen in 7 (quadriplegia unchanged). At 1 year, mean VAS pain scores improved significantly (P < 0.05) from 7.9 (range, 3-10) to 2.8 (range, 0-6). Perioperative complications (non-BMP related) occurred in 2 patients. There were no surgically-related deaths.
rhBMP-2 use, in combination with antibiotics and circumferential instrumented fusion, provides a safe and successful surgical treatment of medically nonresponsive PVO, with solid fusions obtained, good clinical results, and no adverse side effects from the BMP.
•A denitrifying Paenibacillus, designated 79R4, was isolated from the bovine rumen.•Strain 79R4 was selected for enhanced nitrite-metabolizing activity.•Co-addition of strain 79R4 with nitrate to ...rumen cultures decreased methanogenesis.•Co-addition of strain 79R4 with nitrate to rumen cultures detoxified nitrite.•The spore-forming and nitrite-detoxifying ability of 79R4 make it a good probiotic.
The effects of dietary nitrate and Paenibacillus 79R4 (79R4), a denitrifying bacterium, when co-administered as a probiotic, on methane emissions, nitrate and nitrite-metabolizing capacity and fermentation characteristics were studied in vitro. Mixed populations of rumen microbes inoculated with 79R4 metabolized all levels of nitrite studied after 24 h in vitro incubation. Results from in vitro simulations resulted in up to 2 log10 colony forming unit reductions in E. coli O157:H7 and Campylobacter jejuni when these were co-cultured with 79R4. Nitrogen gas was the predominant final product of nitrite reduction by 79R4. When tested with nitrate-treated incubations of rumen microbes, 79R4 inoculation (provided to achieve 106 cells/mL rumen fluid volume) complemented the ruminal methane-decreasing potential of nitrate (P < 0.05) while concurrently increasing fermentation efficiency and enhancing ruminal nitrate and nitrite-metabolizing activity (P < 0.05) compared to untreated and nitrate only-treated incubations.
Assessing perceptions of the COVID-19 vaccines is essential for understanding vaccine hesitancy and for improving uptake during public health emergencies. In the complicated landscape of COVID-19 ...vaccine mandates and rampant misinformation, many individuals faced challenges during vaccination decision-making. The purpose of our mixed methods study is to elucidate factors affecting vaccine decision-making and to highlight the discourse surrounding the COVID-19 vaccines in diverse and underserved communities.
This mixed methods study was conducted in Arizona, Florida, Minnesota, and Wisconsin between March and November 2021, combining a cross-sectional survey (
= 3593) and focus groups (
= 47).
The groups least likely to report receiving a vaccination were non-Hispanic Whites, Indigenous people, males, and those with moderate socioeconomic status (SES). Those indicating high and low SES reported similar vaccination uptake. Focus group data highlighted resistance to mandates, distrust, misinformation, and concerns about the rapid development surrounding the COVID-19 vaccines. Psychological reactance theory posits that strongly persuasive messaging and social pressure can be perceived as a threat to freedom, encouraging an individual to take action to restore that freedom.
Our findings indicate that a subsection of participants felt pressured to get the vaccine, which led to weaker intentions to vaccinate. These results suggest that vaccine rollout strategies should be reevaluated to improve and facilitate informed decision-making.
This work presents a detailed analysis of the diffusion fluxes near and at grain boundaries of irradiated Fe–Cr–Ni alloys, induced by preferential atom-vacancy and atom-interstitial coupling. The ...diffusion flux equations were based on the Perks model formulated through the linear theory of the thermodynamics of irreversible processes. The preferential atom-vacancy coupling was described by the mobility model, whereas the preferential atom-interstitial coupling was described by the interstitial binding model. The composition dependence of the thermodynamic factor was modeled using the CALPHAD approach. The calculated fluxes up to 10 dpa suggested the dominant diffusion mechanism for chromium and iron is via vacancy, while that for nickel can swing from the vacancy to the interstitial dominant mechanism. The diffusion flux in the vicinity of a grain boundary was found to be greatly modified by the segregation induced by irradiation, leading to the oscillatory behavior of alloy compositions in this region.
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