In the first 10 seconds of a core-collapse supernova, almost all of its progenitor's gravitational potential, O(1053 ergs), is carried away in the form of neutrinos. These neutrinos, with O(10 MeV) ...kinetic energy, can interact via coherent elastic neutrino-nucleus scattering (CEνNS) depositing O(1 keV) in detectors. In this work we describe the performances of low-background dark matter detectors, such as LUX-ZEPLIN (LZ), optimized for detecting low-energy depositions, in detecting these neutrino interactions. For instance, a 27 M⊙ supernova at 10 kpc is expected to produce ∼350 neutrino interactions in the 7-tonne liquid xenon active volume of LZ. Based on the LS220 EoS neutrino flux model for a SN, the Noble Element Simulation Technique (NEST), and predicted CEνNS cross-sections for xenon, to study energy deposition and detection of SN neutrinos in LZ. We simulate the response of the LZ data acquisition system (DAQ) and demonstrate its capability and limitations in handling this interaction rate. We present an overview of the LZ detector, focusing on the benefits of liquid xenon for supernova neutrino detection. We discuss energy deposition and detector response simulations and their results. We present an analysis technique to reconstruct the total number of neutrinos and the time of the supernova core bounce.
The electronics of the LUX-ZEPLIN (LZ) experiment, the 10-tonne dark matter detector to be installed at the Sanford Underground Research Facility (SURF), consists of low-noise dual-gain amplifiers ...and a 100-MHz, 14-bit data acquisition system for the TPC PMTs. Pre-prototypes of the analog amplifiers and the 32-channel digitizers were tested extensively with simulated pulses that are similar to the prompt scintillation light and the electroluminescence signals expected in LZ. These studies are used to characterize the noise and to measure the linearity of the system. By increasing the amplitude of the test signals, the effect of saturating the amplifier and the digitizers was studied. The RMS ADC noise of the digitizer channels was measured to be 1.19+ or - 0.01 ADCC. When a high-energy channel of the amplifier is connected to the digitizer, the measured noise remained virtually unchanged, while the noise added by a low-energy channel was estimated to be 0.38 + or - 0.02 ADCC (46 + or - 2 muV). A test facility is under construction to study saturation, mitigate noise and measure the performance of the LZ electronics and data acquisition chain.
The search for dark matter is one of today's most exciting fields. As bigger detectors are being built to increase their sensitivity, background reduction is an ever more challenging issue. To this ...end, a new type of dark matter detector is proposed, a xenon bubble chamber, which would combine the strengths of liquid xenon TPCs, namely event by event energy resolution, with those of a bubble chamber, namely insensitivity to electronic recoils. In addition, it would be the first time ever that a dark matter detector is active on all three detection channels, ionization and scintillation characteristic of xenon detectors, and heat through bubble formation in superheated fluids. Preliminary simulations show that, depending on threshold, a discrimination of 99.99% to 99.9999+% can be achieved, which is on par or better than many current experiments. A prototype is being built at the University at Albany, SUNY. The prototype is currently undergoing seals, thermal, and compression testing.
Purpose: Lepidopteran insect cells are known to exhibit very high radioresistance. Although very effective DNA excision-repair has been proposed as a contributing factor, a detailed understanding of ...insect cell radiation responses has not yet been obtained. Therefore, the study was carried out to understand the in vitro radiation responses of Sf9 lepidopteran cells.
Materials and methods: Exponentially growing asynchronous Sf9 cells (derived from ovaries of Spodoptera frugiperda) were exposed to gamma-radiation doses of 2-200 Gy. Cell survival, growth inhibition, cell cycle progression delay, alterations in cell morphology as well as induction of DNA damage, micronuclei and apoptosis were studied at various post-irradiation time intervals.
Results: Biphasic survival response curves were obtained with D0 rising from 20 Gy (at doses ≤60 Gy) to 85 Gy (between 60 and 200 Gy), corroborating earlier reports on lepidopteran cells. An additional downward deviation at 2 Gy indicated a hypersensitive response. Dose-dependent growth inhibition with a transient G2 delay starting 12 h and extending up to 48-96 h was observed at doses of 10-200 Gy, while a brief G1 S transition delay was observed only at higher doses (≥100 Gy). Significant DNA damage was detected only at 20 Gy and higher doses, in contrast with human cells that showed similar damage at 2 Gy. Interestingly, micronuclei were not induced at any of the doses tested, although spontaneous micronucleation was evident in <1% of cells. Lack of micronucleus induction even at doses that induced significant DNA damage and a transient G2 block (20-50 Gy) strongly indicated a role of holocentric lepidopteran chromosomes. Apoptosis was detected only in a small proportion of cells (3%) exposed to 200 Gy, and cell nucleus size and granularity increased by 72-96 h post-irradiation in a dose-dependent manner. Sf9 nucleoids extracted at 2 M NaCl showed higher compactness than the nucleoids prepared from human cells.
Conclusions: It is clearly shown that lepidopteran cells are highly resistant to the induction of DNA damage and micronuclei, and display very low induction of apoptosis at doses up to 200 Gy. While the lack of micronucleus induction seems to be primarily due to the holocentric nature of their chromosomes, certain unique signalling pathways might be responsible for the low induction of apoptosis. Factors causing protection of Sf9 cellular DNA from radiation-induced damage are presently being investigated.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Multicellular spheroids, an appropriate in vitro system for simulating 3-D tumor micro-milieu can be used for evaluating and predicting tumor response to therapeutic agents including metabolic ...inhibitors. However, detailed understanding of the nature, distribution and sensitivity/responses of cellular sub-populations to potential therapeutic agents/strategies is required for using this unique model with optimal precision. Spheroid characteristics may also vary considerably with the origin and type of cell line used, and thorough characterization of viable and dissociated glioma cell spheroids is not yet completely known. In order to evaluate in vivo responses of gliomas to various therapeutic strategies, especially the metabolic inhibitors capable of penetrating the blood brain barrier, we have characterized continuously growing spheroids of a human glioma cell line (BMG-1) with respect to organization, growth, viability, cell survival, cell death, metabolic and mitochondrial status, oxidative stress and radiation response using microscopy, flow cytometry and enzymatic assays. Spheroids were fed daily with fresh medium in order to maintain nutrient supply to outer cellular layers while hypoxia/necrosis developed in the innermost cells of enlarging spheroids.
Volume of spheroids, fed daily with fresh medium, increased exponentially during 7-28 days of growth through three population doublings. Proportion of G1-phase cells was higher (approximately 60%) than exponentially growing monolayer cells (approximately 48%). A significant fraction of S-phase cells turned metabolically inactive (disengaged in DNA synthesis) with increasing age of the spheroids, unlike in quiescent monolayer cultures, where the fraction of S-phase cells was less than 5%. With increasing spheroid size, increasing sub-populations of cells became non-viable and entered apoptosis or necrosis revealed by Annexin-V-FITC/PI staining. PI positive (necrotic) cells were not confined to the centre of the spheroid, but distributed at certain discrete foci. Average glucose consumption and lactate production were 2-3 folds higher in viable spheroid cells compared to monolayer cells, implying a compensatory increase in glycolysis possibly due to hypoxic environment. HIF-1alpha was expressed only in spheroids and increased in an age-dependent manner, whereas c-Myc (known to induce apoptosis in glucose-deprived cells) levels were three times higher than monolayer cells. Mitochondrial mass and activity decreased significantly during first 14 days of growth but increased with age, and were not associated with increase in ROS levels. Bcl-2 and Bax levels were higher (approximately 2 folds) than monolayers, while the ratio (Bcl/Bax) remained unaltered. Radiation-induced oxidative stress was considerably less in spheroids as compared to monolayers, and corresponded well with increase in radioresistance demonstrated by the clonogenic assay, similar to hypoxia induced radioresistance observed in tumors.
Development of S-negative cells and reduced endogenous and radiation-induced ROS coupled with higher levels of anti (Bcl2) as well as pro (Bax) apoptotic regulators observed in spheroids suggest the intricate/complex nature of endogenous as well as induced stress resistance that could exist in tumors, which contribute to the treatment resistance.
Dual-phase xenon detectors, as currently used in direct detection dark matter experiments, have observed elevated rates of background electron events in the low energy region. While this background ...negatively impacts detector performance in various ways, its origins have only been partially studied. In this paper we report a systematic investigation of the electron pathologies observed in the LUX dark matter experiment. Here, we characterize different electron populations based on their emission intensities and their correlations with preceding energy depositions in the detector. By studying the background under different experimental conditions, we identified the leading emission mechanisms, including photoionization and the photoelectric effect induced by the xenon luminescence, delayed emission of electrons trapped under the liquid surface, capture and release of drifting electrons by impurities, and grid electron emission. We discuss how these backgrounds can be mitigated in LUX and future xenon-based dark matter experiments.
Abstract
Background: Despite great advances in understanding the etiology and molecular biology of breast cacncers, the treatment options for patients affected with this disease remain severly ...limited. The KCNMA1, which encodes the pore forming α-subunit of large-conductance calcium-activated voltage-sensitive potassium (BKCa) channel, may play highly critical roles in breast tumor cells metastasis and angiogenesis within the brain. We sought to investigate the above roles of KCNMA1 using breast tumor models.Methods: We validated the results from the breast tumor cell lines data with human normal breast tissue, primary, non-metastatic and metastatic breast tumors by RT-PCR. The KCNMA1 was cloned into mammalian expression vector (pcDNA6). MCF-7 cells (non-metastatic, KCNMA1 low expressing) and HEK cells (null type for KCNMA1) were transfected with pcDNA6/KCNMA1 and stable clones selected. The expression of KCNMA1 was confirmed using RT-PCR, western blot and qPCR. The biological role of KCNMA1 was studied using parental and transfected MCF-7 cells by cell proliferation, matrigel invasion, transendothelial migration and membrane potential assays in vitro and tumorogenecity and angiogenesis using subcutaneous xenograft mouse model. To study the role of KCNMA1 in angiogenesis, human brain microvascular endothelial cells (HCMEC/D3) were co cultured with breast tumor cells and VEGF levels determined by ELISA.Results: The KCNMA1 was overexpressed in metastatic breast tumor samples compared to primary breast tumor. Stably transfected HEK and MCF-7 cells showed 2.5 to 3-fold increase in KCNMA1 mRNA expression, which corroborated with the increased protein levels and BKCa channel activity. In addition MCF-7 cells expressing KCNMA1 showed a five-fold increase in invasion while a two-fold increase in TEM was observed compared to parental MCF-7 cells. A marked increase in the proliferation rate of KCNMA1-transfected cells compared to MCF-7 alone was observed, suggesting that KCNMA1 has a profound effect on breast cancer cell proliferation. A two-fold increase in VEGF secretion in KCNMA1-overexpressing MCF-7 cells was observed. The results also indicated that the conditioned media from MCF-7 cells increased BKCa channel expression in HCMEC/D3 cells by nearly 1.5-fold as compared to HCMEC/D3 cells cultured without the conditioned media. The proliferation of HCMEC/D3 cells was increased by three-folds in the presence of VEGF or conditioned media from MCF-7 overexpressing KCNMA1. The proliferation was attenuated by BKCa channels inhibitor (Iberiotoxin). The in vitro results were validated using subcutaneous mouse model experiment. We found statistically significant increase in mean tumor volume in mice with KCNMA1-transfected MCF-7 cells compared with parental cells.Conclusions: Our results clearly show that KCNMA1 promotes breast cancer cell invasion, and possibly metastasis. Taken together these experiments showed a critical role of KCNMA1 expression on VEGF secretion by MCF-7 cells and endothelial cell proliferation. These studies will contribute to a fundamental understanding of the role of KCNMA1 in metastatic breast cancer biology and angiogenesis.
Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6165.
Abstract
Background: We have recently shown that KCNMA1, which encodes the pore forming α-subunit of large-conductance calcium-activated voltage-sensitive potassium (BKCa) channel, plays a highly ...critical role in breast tumor cells metastatic to brain and somewhat less critical role in primary breast cancer cell metastasis. The resulting functional heterogeneity of BKCa channels is attributed generally to alternative splicing of KCNMA1 that generate BKCa channel isoform with altered channel properties. We have identified a KCNMA1 splice variant (KCNMA1vE22) expressed in breast cancer cell line (MDA-MB-361) metastatic to brain with a deletion of 108 bp in exon 22 between the S9 and S10 protein subunit (C-terminus). In this study we investigated the biological function of KCNMA1vE22 in vitro and in vivo.Methods: We validated the results from the breast tumor cell lines data with human normal breast tissue, primary, non-metastatic and metastatic breast tumors by RT-PCR. The KCNMA1vE22 was identified from A-172 tumor cells and cloned into mammalian expression vector (pcDNA6). MCF-7 cells (non-metastatic, null type for KCNMA1vE22) and HEK cells (null type for KCNMA1 and KCNMA1vE22) were transfected with pcDNA6/KCNMA1vE22 and stable clones selected. The expression of KCNMA1 and KCNMA1vE22 was confirmed using RT-PCR, western blot and qPCR. The biological role of the splice variant was studied using parental and transfected MCF-7 cells by cell proliferation, matrigel invasion, transendothelial migration and membrane potential assays in vitro and tumorogenecity using s.c xenograft mouse model.Results: Based on the preliminary screening of breast tumor samples, KCNMA1vE22 was undetectable in primary as well as systemic metastatic breast tumor samples. Stably transfected HEK and MCF-7 cells showed 2.5 to 3-fold increase in KCNMA1 mRNA expression, which corroborated with the increased protein levels and BKCa channel activity. In addition MCF-7 cells expressing KCNMA1vE22 showed a eight-fold increase in invasion while a three-fold increase in TEM was observed compared to parental MCF-7 cells. A marked increase in the proliferation rate of KCNAM1vE22-transfected cells compared to MCF-7 alone was observed, suggesting that KCNAM1vE22 has a profound effect on breast cancer cell proliferation. The in vitro results were validated by subcutaneous mouse model experiment. We found statistically significant increase in mean tumor volume in mice with KCNMA1vE22 transfected compared with parental MCF-7 cells.Conclusions: Our results clearly show that KCNMA1vE22 promotes breast cancer cell invasion, and possibly metastasis to brain. Perhaps the discovery and validation of brain specific metastasis-associated KCNMA1 alternate splice variants will serve as new tools for the diagnosis and classification of breast tumor patients with high risk of brain metastasis. The variant KCNMA1vE22 that we have discovered potentially may fill the gap to serve as a new generation of biomarker of breast cancer metastasis to brain.
Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6166.
Weakly interacting massive particles (WIMPs) are a leading candidate for dark matter and are expected to produce nuclear recoil (NR) events within liquid xenon time-projection chambers. We present a ...measurement of the scintillation timing characteristics of liquid xenon in the LUX dark matter detector and develop a pulse shape discriminant to be used for particle identification. To accurately measure the timing characteristics, we develop a template-fitting method to reconstruct the detection times of photons. Analyzing calibration data collected during the 2013–2016 LUX WIMP search, we provide a new measurement of the singlet-to-triplet scintillation ratio for electron recoils (ER) below 46 keV, and we make, to our knowledge, a first-ever measurement of the NR singlet-to-triplet ratio at recoil energies below 74 keV. We exploit the difference of the photon time spectra for NR and ER events by using a prompt fraction discrimination parameter, which is optimized using calibration data to have the least number of ER events that occur in a 50% NR acceptance region. We then demonstrate how this discriminant can be used in conjunction with the charge-to-light discrimination to possibly improve the signal-to-noise ratio for nuclear recoils.
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