6,232 research outputs found

    Influence of pH and temperature on alunite dissolution: Rates, products and insights on mechanisms from atomistic simulation

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    This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe processes, rates, controlling factors and products of alunite (KAl3(SO4)2(OH)6) dissolution were assessed using batch dissolution experiments at pHs of c. 3, 4, 4.6, 7 and 8, and temperatures of c. 280, 293 and 313K. Alunite dissolution is roughly congruent at pH3, while at pH≥3.9 the process is incongruent, giving a lower Al/K ratio in solution than in the pristine alunite sample. The decrease in the Al/K ratio appears to be caused by precipitation of secondary aluminium sulfate/hydroxysulfate minerals coating the surface of the dissolving alunite, as inferred from SEM images and XPS determinations, but these minerals do not passivate the alunite surface for the time frame of the experiments (up to 400h). The lowest dissolution rates are obtained for pH4.6 and 280K. Both the temperature increase and any pH variation from that point lead to faster dissolution rates. Based on the potassium release to solution, the influence of pH and temperature on the alunite dissolution rate for pH of 4.8 and below can be expressed as;. rateK= 104.4 ± 0.5aH+0.10 ± 0.02e32±3/RTwhere rateKis the alunite dissolution rate (in mol·m-2·s-1); aH+is the activity of hydrogen ions in solution; R is the Universal gas constant (in kJ·mol-1·K-1) and T is temperature (in K).For pH of 4.6 and above, the alunite dissolution rate can instead be expressed as;. rateK= 102.5±0.8aOH0.14±0.02e-39±4/RTwhere aOH-is the activity of hydroxyl ions in solution. In light of the calculated values for the activation energy under the two sets of pH conditions (32 ± 3 and 39 ± 4 kJ·mol-1), alunite dissolution appears to be surface-controlled. Examination of the most stable solvated alunite surfaces obtained by atomistic computer simulations suggests that the least energetically favourable steps during alunite dissolution are the detachment of either Al atoms or SO4tetrahedra from exposed surfaces. Thus, these processes are most probably the rate-determining steps in alunite dissolution.This work has been funded by the EC Marie Curie Intra-European Fellowship program (Project entitled ‘Reactivity of Aluminium Sulfate Minerals in Mine Wastes’; RASMIM) through a fellowship to P.A. The authors acknowledge also the NERC (National Environmental Research Council, United Kingdom) for partially funding the characterisation of mineral samples through the project ‘Characterisation of nanometre-sized aluminium sulphates: implications for mobility of aluminium from mine wastes’ (FENAC/2013/11/001)

    The androgen receptor and signal-transduction pathways in hormone-refractory prostate cancer. Part 2: androgen-receptor cofactors and bypass pathways

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    Prostate cancer is the second leading cause of cancer related deaths in men from the western world. Treatment of prostate cancer has relied on androgen deprivation therapy for the past 50 years. Response rates are initially high (70-80%), however almost all patients develop androgen escape and subsequently die within 1-2 years. Unlike breast cancer, alternative approaches (chemotherapy and radiotherapy) do not increase survival time. The high rate of prostate cancer mortality is therefore strongly linked to both development of androgen escape and the lack of alternate therapies. AR mutations and amplifications can not explain all cases of androgen escape and post-translational modification of the AR has become an alternative theory. However recently it has been suggested that AR co-activators e.g. SRC-1 or pathways the bypass the AR (Ras/MAP kinase or PI3K/Akt) may stimulated prostate cancer progression independent of the AR. This review will focus on how AR coactivators may act to increase AR transactivation during sub-optimal DHT concentrations and also how signal transduction pathways may promote androgen escape via activation of transcription factors, e.g. AP-1, c-Myc and Myb, that induce cell proliferation or inhibit apoptosis

    Spatial distribution and energy release of nonvolcanic tremor at Parkfield, California

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    Nonvolcanic tremors (NVTs) are observed in transition zones between freely slipping andlocked sections of faults and normally occur below the seismogenic zone. Based on NVT recordings in theParkfield region of the San Andreas Fault, we provide a novel approach to assess the energy release of theseevents and assign magnitudes (Me) that are compatible with size estimates of small earthquakes in the sameregion. To assess the energy magnitude of a detected tremor, we refine the estimate of its duration andperform a spectral analysis that accounts for local attenuation. For the 218 NVTs that we were able to process,we resolveMevalues in the range of 0.67 to 0.84. For events, which we could not process using the spectralanalysis technique, we propose a statistical model to estimateMevalues using observable characteristics,such as peak amplitude, spectral velocity at the source corner frequency, and duration. We furthermoreprovide seismic moment and moment magnitude estimates and calculate stress drops in a range of 3–10 kPa.As a result of our spectral analyses, wefind strong indications regarding the ongoing debate aboutpotential NVT location hypotheses: the Parkfield NVTs have a higher probability to be located in the proposedthree-dimensional cloud-like cluster than in any other suggested location distributi

    Visual kinematic force estimation in robot-assisted surgery – application to knot tying

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    Robot-assisted surgery has potential advantages but lacks force feedback, which can lead to errors such as broken stitches or tissue damage. More experienced surgeons can judge the tool-tissue forces visually and an automated way of capturing this skill is desirable. Methods to measure force tend to involve complex measurement devices or visual tracking of tissue deformation. We investigate whether surgical forces can be estimated simply from the discrepancy between kinematic and visual measurement of the tool position. We show that combined visual and kinematic force estimation can be achieved without external measurements or modelling of tissue deformation. After initial alignment when no force is applied to the tool, visual and kinematic estimates of tool position diverge under force. We plot visual/kinematic displacement with force using vision and marker-based tracking. We demonstrate the ability to discern the forces involved in knot tying and visualize the displacement force using the publicly available JIGSAWS dataset as well as clinical examples of knot tying with the da Vinci surgical system. The ability to visualize or feel forces using this method may offer an advantage to those learning robotic surgery as well as adding to the information available to more experienced surgeons

    Wolbachia endosymbionts induce neutrophil extracellular trap formation in human onchocerciasis

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    The endosymbiotic bacteria, Wolbachia, induce neutrophilic responses to the human helminth pathogen Onchocerca volvulus. The formation of Neutrophil Extracellular Traps (NETs), has been implicated in anti-microbial defence, but has not been identified in human helminth infection. Here, we demonstrate NETs formation in human onchocerciasis. Extracellular NETs and neutrophils were visualised around O. volvulus in nodules excised from untreated patients but not in nodules from patients treated with the anti-Wolbachia drug, doxycycline. Whole Wolbachia or microspheres coated with a synthetic Wolbachia lipopeptide (WoLP) of the major nematode Wolbachia TLR2/6 ligand, peptidoglycan associated lipoprotein, induced NETosis in human neutrophils in vitro. TLR6 dependency of Wolbachia and WoLP NETosis was demonstrated using purified neutrophils from TLR6 deficient mice. Thus, we demonstrate for the first time that NETosis occurs during natural human helminth infection and demonstrate a mechanism of NETosis induction via Wolbachia endobacteria and direct ligation of Wolbachia lipoprotein by neutrophil TLR2/6

    Diffuse White Matter Signal Abnormalities on Magnetic Resonance Imaging Are Associated With Human Immunodeficiency Virus Type 1 Viral Escape in the Central Nervous System Among Patients With Neurological Symptoms

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    Background: Human immunodeficiency virus type 1 (HIV-1) can replicate independently in extravascular compartments such as the central nervous system, resulting in either cerebrospinal fluid (CSF) discordance (viral load [VL] in CSF 0.5 log10 copies HIV-1 RNA greater than plasma VL) or escape (detection of HIV VL >50 copies/mL in CSF in patients with suppressed plasma VL <50 copies/mL). Both discordance and escape may be associated with neurological symptoms. We explored risk factors for CSF discordance and escape in patients presenting with diverse neurological problems. Methods: HIV-infected adult patients undergoing diagnostic lumbar puncture (LP) at a single center between 2011 and 2015 were included in the analysis. Clinical and neuroimaging variables associated with CSF discordance/escape were identified using multivariate logistic regression. Results: One hundred forty-six patients with a median age of 45.3 (interquartile range [IQR], 39.6–51.5) years underwent 163 LPs. Median CD4 count was 430 (IQR, 190–620) cells/µL. Twenty-four (14.7%) LPs in 22 patients showed CSF discordance, of which 10 (6.1%) LPs in 9 patients represented CSF escape. In multivariate analysis, both CSF discordance and escape were associated with diffuse white matter signal abnormalities (DWMSAs) on cranial magnetic resonance imaging (adjusted odds ratio, 10.3 [95% confidence interval {CI}, 2.3–45.0], P = .007 and 56.9 [95% CI, 4.0–882.8], P = .01, respectively). All 7 patients with CSF escape (10 LPs) had been diagnosed with HIV >7 years prior to LP, and 6 of 6 patients with resistance data had documented evidence of drug-resistant virus in plasma. Conclusions: Among patients presenting with diverse neurological problems, CSF discordance or escape was observed in 15%, with treatment-experienced patients dominating the escape group. DWMSAs in HIV-infected individuals presenting with neurological problems should raise suspicion of possible CSF discordance/escape

    Is the biology of breast cancer changing? A study of hormone receptor status 1984-1986 and 1996-1997

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    Using archived tumours, those from 1984-1986 and 1996-1997 underwent immunohistochemistry for hormone receptors and grade analysis. A significant shift towards more ER-positive and low-grade disease was found; this appears to reflect screening practices, but could still influence survival

    Developing collaboration skills in first year undergraduate business students

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    Collaboration skills are defined as the set of skills and capabilities required to work effectively within and across groups to achieve group goals. The development of these skills are assumed but not taught directly or evaluated in undergraduate group assessments in many university subjects. This paper discusses a research project investigating the development of student collaboration skills in the compulsory first year undergraduate subject 21129 Managing People and Organisations. One of the key aims of the subject is to help students understand and acquire a range of collaboration skills that will enhance their work readiness. During August 2008, 290 student surveys were completed by students after their initial formation into groups during tutorials. These surveys asked students about their past experiences of group work, and their expectations and motivations with respect to group work in this subject over the coming semester. A follow-up survey was conducted in November, and attempts to capture the extent of changes, if any, in student perceptions of their experience developing collaboration skills over the semester. This paper reports on the findings of stage one of this project. An overview of student attitudes and perceptions is presented, as well as findings on the systematic variation of these with respondent characteristics. The finding of a number of statistically significant associations of student satisfaction with the method of group formation employed in tutorials is then discussed as a surprise finding from this research

    Health care logistics: who has the ball during disaster?

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    In contemporary organizations, a wide gamut of options is available for sustaining and supporting health care operations. When disaster strikes, despite having tenable plans for routine replenishment and operations, many organizations find themselves ill-prepared, ill-equipped, and without effective mechanisms in place to sustain operations during the immediate aftermath of a crisis. Health care operations can be abruptly halted due to the non-availability of supply
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