778 research outputs found
Hydraulic fracturing propagation mechanism during shale gas reservoir stimulation through horizontal well
NaÄin razlamanja stijenske mase u naslagama naftnih Å”kriljaca jedan je od glavnih Äimbenika koji djeluju na uÄinkovitost hidrauliÄkog frakturiranja (frakiranja). U ovom su radu provedena fizikalna ispitivanja i numeriÄko modeliranje u svrhu sustavnog ispitivanja uÄinka in-situ (podzemnog) naprezanja i kuta buÅ”enja na stvaranje tlaka zbog hidrauliÄkog frakturiranja, Å”irenje razlamanja i naÄin razlamanja u horizontalnoj buÅ”otini naftnog nalaziÅ”ta Shengli u Luojia pokrajini, u izvoÄenju Sinopec Corp. Ukupno je razmatrano Å”est razliÄitih in-situ kombinacija naprezanja i osam razliÄitih kutova buÅ”enja slojevite stijenske mase tijekom hidrauliÄkog frakturiranja. Sažetak nastanka i Å”irenja pukotine te zavrÅ”ni oblici pukotina nastalih hidrauliÄkim frakturiranjem u slojevitim stijenskim masama otkrivaju da kod stratificiranih stijena s istim kutom buÅ”enja, Å”to je veÄi in-situ omjer naprezanja (t.j. niže maksimalno horizontalno osnovno naprezanje pri konstantnim vertikalnim naprezanjem), potreban je niži hidrauliÄki tlak za poticanje i Å”irenje hidrauliÄkog frakturiranja. Å toviÅ”e, ustanovljeno je da je kod stratificirane stijenske mase pri istom omjeru naprezanja, tlak hidrauliÄkog frakturiranja, u sluÄaju kad je kut buÅ”enja 30Ā°, veÄi nego u svim drugim sluÄajevima. Nadalje, zapaženo je da uÄinak stratifikacije na hidrauliÄko frakturiranje postaje slabiji s porastom in-situ omjera naprezanja. KonaÄno je zakljuÄeno da rezultati ove analize mogu biti važan teorijski pokazatelj u poboljÅ”anju oblikovanja hidrauliÄkog frakturiranja kako bi se osiguralo uÄinkovito stimuliranje naslaga naftnih Å”kriljaca.The fracture pattern of rock mass in shale gas reservoirs is one of the main factors affecting the efficiency of hydraulic fracturing. In this paper, physical experiments and numerical modelling were conducted to systematically investigate the effect of the in-situ stress and perforation angle on the hydraulic fracture initiation pressure and location, fracture propagation, and fracture pattern in a horizontal well drilled by Sinopec Corp. in Luojia area of Shengli Oilfield. A total of six different in-situ stress combinations and eight different perforation angles were considered for the stratified rock mass during the hydraulic fracturing. A summary of the fracture initiations and propagation, and the final fracture patterns induced by the hydraulic fracturing in the stratified rock masses reveals that, for the stratified rock masses with the same perforation angle, the larger the in-situ stress ratio (i.e. lower maximum horizontal principal stress when the vertical stress remains constant) is, the lower hydraulic pressure is required for hydraulic fracturing initiation and propagation. Moreover, it is found that, for the stratified rock mass under the same stress ratio, the hydraulic fracturing pressure in the case with a perforation angle of 30Ā° is higher than that in all other cases. Furthermore, it is noted that the effect of the stratification on the hydraulic fracturing becomes weaker with the in-situ stress ratio increasing. It is finally concluded that the results from this study can provide important theoretical guidance for improving the hydraulic fracturing design in order to ensure the effective shale gas reservoir stimulations
Observation of Majorana fermions with spin selective Andreev reflection in the vortex of topological superconductor
Majorana fermion (MF) whose antiparticle is itself has been predicted in
condensed matter systems. Signatures of the MFs have been reported as zero
energy modes in various systems. More definitive evidences are highly desired
to verify the existence of the MF. Very recently, theory has predicted MFs to
induce spin selective Andreev reflection (SSAR), a novel magnetic property
which can be used to detect the MFs. Here we report the first observation of
the SSAR from MFs inside vortices in Bi2Te3/NbSe2 hetero-structure, in which
topological superconductivity was previously established. By using
spin-polarized scanning tunneling microscopy/spectroscopy (STM/STS), we show
that the zero-bias peak of the tunneling differential conductance at the vortex
center is substantially higher when the tip polarization and the external
magnetic field are parallel than anti-parallel to each other. Such strong spin
dependence of the tunneling is absent away from the vortex center, or in a
conventional superconductor. The observed spin dependent tunneling effect is a
direct evidence for the SSAR from MFs, fully consistent with theoretical
analyses. Our work provides definitive evidences of MFs and will stimulate the
MFs research on their novel physical properties, hence a step towards their
statistics and application in quantum computing.Comment: 4 figures 15 page
WC@meso-Pt coreāshell nanostructures for fuel cells
We developed a facile method to synthesize coreāshell WC@meso-Pt nanocatalysts by carburizing ammonium tungstate and copper nitrate via gasāsolid reactions, followed by a Pt replacement reaction. The mesoporous nanocomposite displays higher activity and stability towards methanol electrooxidation than commercial Pt/C catalysts
Experimental Realization of Weyl Exceptional Rings in a Synthetic Three-Dimensional Non-Hermitian Phononic Crystal
Weyl points (WPs) are isolated degeneracies carrying quantized topological
charges, and are therefore robust against Hermitian perturbations. WPs are
predicted to spread to the Weyl exceptional rings (WERs) in the presence of
non-Hermiticity. Here, we use a one-dimensional (1D) Aubry-Andre-Harper (AAH)
model to construct a Weyl semimetal in a 3D parameter space comprised of one
reciprocal dimension and two synthetic dimensions. The inclusion of
non-Hermiticity in the form of gain and loss produces a WER. The topology of
the WER is characterized by both its topological charge and non-Hermitian
winding numbers. The WER is experimentally observed in a 1D phononic crystal
with the non-Hermiticity introduced by active acoustic components. In addition,
Fermi arcs are observed to survive the presence of non-Hermitian effect. We
envision our findings to pave the way for studying the high-dimensional
non-Hermitian topological physics in acoustics.Comment: 14 pages, 5 figure
Hydroxysafflor Yellow A protects spinal cords from ischemia/reperfusion injury in rabbits
<p>Abstract</p> <p>Background</p> <p>Hydroxysafflor Yellow A (HSYA), which is one of the most important active ingredients of the Chinese herb <it>Carthamus tinctorius L</it>, is widely used in the treatment of cerebrovascular and cardiovascular diseases. However, the potential protective effect of HSYA in spinal cord ischemia/reperfusion (I/R) injury is still unknown.</p> <p>Methods</p> <p>Thirty-nine rabbits were randomly divided into three groups: sham group, I/R group and HSYA group. All animals were sacrificed after neurological evaluation with modified Tarlov criteria at the 48th hour after reperfusion, and the spinal cord segments (L4-6) were harvested for histopathological examination, biochemical analysis and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining.</p> <p>Results</p> <p>Neurological outcomes in HSYA group were slightly improved compared with those in I/R group. Histopathological analysis revealed that HSYA treatment attenuated I/R induced necrosis in spinal cords. Similarly, alleviated oxidative stress was indicated by decreased malondialdehyde (MDA) level and increased superoxide dismutase (SOD) activity after HSYA treatment. Moreover, as seen from TUNEL results, HSYA also protected neurons from I/R-induced apoptosis in rabbits.</p> <p>Conclusions</p> <p>These findings suggest that HSYA may protect spinal cords from I/R injury by alleviating oxidative stress and reducing neuronal apoptosis in rabbits.</p
Fabricating core-shell WC@C/Pt structures and its enhanced performance for methanol electrooxidation
Ā© 2017 Chinese Physical Society. The spray-dried spheres within a W/Pt multi-separation can be used to prepare discrete core-shell WC@C/Pt catalysts through a typical carburization production mechanism at 800 Ā°C. In contrast with previous studies of the WC/Pt synthesis, the reaction observed here proceeds through an indirect annealing mechanism at 600 Ā°C wherein species diffuse, thereby resulting in core-shell structure, and Pt nanoparticles were successfully dispersed in size/shape and randomly scattered across the in situ produced C spheres. Through direct carburization or at higher initial hydrochloroplatinic acid concentrations, however, complete reaction with core-shell spheres was not observed. Indirect carburization reduces the strain felt by the bonds featuring the larger WC particles and allows the motion of carbon around WC and Pt nanoparticles to be reserved, influencing the electrocatalytic performance and stability toward methanol oxidation
Quality of reporting of systematic reviews published in āevidence-basedā Chinese journals
BACKGROUND: The number of systematic reviews (SRs)/meta-analyses (MAs) has increased dramatically in China over the past decades. However, evaluation of quality of reporting of systematic reviews published has not been undertaken. The objective of this study is to evaluate the quality of reporting of SRs/MAs assessing efficacy and/or harms of clinical interventions published in āevidence-basedā Chinese journals. METHODS: Web-based database searches were conducted for the Chinese Journal of Evidence-based Medicine, the Journal of Evidence-Based Medicine, the Chinese Journal of Evidence Based Pediatrics, and the Chinese Journal of Evidence-Based Cardiovascular Medicine. SRs/MAs assessing efficacy and/or harms of clinical interventions were included. The cut-off was December 31st 2011. The PRISMA statement was applied to assess the quality of reporting. Each item was assessed as follows: āYesā for total compliance, scored ā1ā; āpartialā for partial compliance, scored ā0.5ā; and āNoā for non-compliance, scored ā0ā. The review was considered to have major flaws if it received a total score of ā¤15.0, minor flaws if it received a total score of 15.5 to 21.0, and minimal flaws if it received a total score 21.5 to 27.0. Odds ratios were used for binary variables, and the mean difference was used for continuous variables. Analyses were performed using RevMan 5.0 software. RESULTS: Overall, 487 SRs/MAs were identified and assessed. The included reviews had medium quality with minor flaws based on PRISMA total scores (range: 8.5ā26.0; mean: 19.6āĀ±ā3.3). The stratified analysis showed that SRs/MAs with more than 3 authors, from a university, hospitalā+āuniversity cooperation, multiple affiliations (ā„2), and funding have significantly higher quality of reporting of SRs/MAs; 58% of the included reviews were considered to have minor flaws (total score of 15.6 to 21.0). Only 9.6% of reviews were considered to have major flaws. Specific areas needing improvement in reporting include the abstract, protocol and registration, and characteristics of the search. CONCLUSIONS: The reporting of SRs published in āevidence-basedā Chinese journals is poor and needs to be improved in order for reviews to be useful. SR authors should use the PRISMA checklist to ensure complete and accurate accounts of their SRs
Asymmetric Inelastic Inert Doublet Dark Matter from Triplet Scalar Leptogenesis
The nature of dark matter (DM) particles and the mechanism that provides
their measured relic abundance are currently unknown. In this paper we
investigate inert scalar and vector like fermion doublet DM candidates with a
charge asymmetry in the dark sector, which is generated by the same mechanism
that provides the baryon asymmetry, namely baryogenesis-via-leptogenesis
induced by decays of scalar triplets. At the same time the model gives rise to
neutrino masses in the ballpark of oscillation experiments via type II seesaw.
We discuss possible sources of depletion of asymmetry in the DM and visible
sectors and solve the relevant Boltzmann equations for quasi-equilibrium decay
of triplet scalars. A Monte-Carlo-Markov-Chain analysis is performed for the
whole parameter space. The survival of the asymmetry in the dark sector leads
to inelastic scattering off nuclei. We then apply bayesian statistic to infer
the model parameters favoured by the current experimental data, in particular
the DAMA annual modulation and Xenon100 exclusion limit. The latter strongly
disfavours asymmetric scalar doublet DM of mass \mathcal{O}(\TeV) as required
by DM- oscillations, while an asymmetric vector like fermion
doublet DM with mass around 100 GeV is a good candidate for DAMA annual
modulation yet satisfying the constraints from Xenon100 data.Comment: 35 pages and 15 figures, references adde
Transcription phase, protein characteristics of DEV UL45 and prokaryotic expression, antibody preparation of the UL45 des-transmembrane domain
<p>Abstract</p> <p>Background</p> <p>Some UL45 gene function of Herpesvirus was reported. While there was no any report of the duck enteritis virus (DEV) UL45 protein as yet.</p> <p>Results</p> <p>The UL45 gene and des-transmembrane domain of UL45 (named UL45Ī gene, 295-675bp of UL45) of DEV were amplified by PCR and subcloned into the prokaryotic expression vector pET-32a(+). The constructed recombinant plasmids were transformed into the host strain BL21(DE3) PLysS and induced by IPTG. SDS-PAGE analysis showed the UL45 gene couldn't express while UL45Ī gene was highly expressed. His Purify Kit or salting-out could purify the protein effectively. Using the purified protein to immunize New-Zealand rabbits and produce polyclonal antibody. The agar diffusion reaction showed the titer of antibody was 1:32. Western blot analysis indicated the purified rabbit anti-UL45Ī IgG had a high level of specificity and the UL45 gene was a part of DEV genome. The transcription phase study of UL45 gene showed that expression of UL45 mRNA was at a low level from 0 to 18 h post-infection (pi), then accumulated quickly at 24 h pi and peaked at 42 h pi. It can be detected till 72 h pi. Besides, western blot analysis of purified virion and different viral ingredients showed that the UL45 protein resided in the purified virion and the viral envelope.</p> <p>Conclusions</p> <p>The rabbit anti-UL45Ī IgG was produced successfully and it can serve as a good tool for penetrating studies of the function of DEV UL45 protein. The transcription phase and protein characteristics analysis indicated that DEV UL45 gene was a late gene and UL45 protein may be a viral envelope protein.</p
Effects of tumor metabolic microenvironment on regulatory T cells
Recent studies have shown that on one hand, tumors need to obtain a sufficient energy supply, and on the other hand they must evade the bodyās immune surveillance. Because of their metabolic reprogramming characteristics, tumors can modify the physicochemical properties of the microenvironment, which in turn affects the biological characteristics of the cells infiltrating them. Regulatory T cells (Tregs) are a subset of T cells that regulate immune responses in the body. They exist in large quantities in the tumor microenvironment and exert immunosuppressive effects. The main effect of tumor microenvironment on Tregs is to promote their differentiation, proliferation, secretion of immunosuppressive factors, and chemotactic recruitment to play a role in immunosuppression in tumor tissues. This review focuses on cell metabolism reprogramming and the most significant features of the tumor microenvironment relative to the functional effects on Tregs, highlighting our understanding of the mechanisms of tumor immune evasion and providing new directions for tumor immunotherapy
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