Reaction Threshold Research Articles

The Mechanism of Graphene Vapor-Solid Growth on Insulating Substrates.

Wafer-scale single-crystal graphene film directly grown on insulating substrates via the chemical vapor deposition (CVD) method is desired for building high-performance graphene-based devices. In comparison with the well-studied mechanism of graphene growth on transition metal substrates, the lack of understanding on the mechanism of graphene growth on insulating surfaces greatly hinders the progress. Here, by using first-principles calculation, we systematically explored the absorption of various carbon species CHx (x = 0, 1, 2, 3, 4) on three typical insulating substrates [h-BN, sapphire, and quartz] and reveal that graphene growth on an insulating surface is dominated by the reaction of active carbon species with the hydrogen-passivated graphene edges and thus is less sensitive to the type of the substrate. The dominating gas phase precursor, CH3, plays two key roles in graphene CVD growth on an insulating substrate: (i) to feed the graphene growth and (ii) to remove excessive hydrogen atoms from the edge of graphene. The threshold reaction barriers for the growth of graphene armchair (AC) and zigzag (ZZ) edges were calculated as 3.00 and 1.94 eV, respectively; thus the ZZ edge grows faster than the AC one. Our theory successfully explained why the circumference of a graphene island grown on insulating substrates is generally dominated by AC edges, which is a long-standing puzzle of graphene growth. In addition, the very slow graphene growth rate on an insulating substrate is calculated and agrees well with existing experimental observations. The comprehensive insights on the graphene growth on insulating surfaces at the atomic scale provide guidance on the experimental design for high-quality graphene growth on insulating substrates.

Prognostic Value of "Cycle Threshold" in Confirmed COVID-19 Patients.

Objective: To study the correlation between the cycle threshold (CT) of reverse transcription–polymerase chain reaction (RT–PCR) test in confirmed COVID-19 patients and the severity of disease.Background: RT–PCR test is a standard method for the diagnosis of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections. This test is based upon the amplification of the fluorescent signal. The number of cycles that the fluorescent signal undergoes to reach the threshold is called “cycle threshold.” It is inversely related to the nucleic acid content of the sample.Patients and methods: This is a single-centered, retrospective observational study. We have included a total of 192 patients. SARS-CoV-2 infection was confirmed by the RT–PCR test. Entire data have been collected from the electronic medical records.The primary outcome was 28-day mortality, whereas the secondary outcomes were intensive care unit (ICU) admission, invasive ventilation, acute kidney injury, renal replacement therapy (RRT), shock, and COVID-19 reporting and data system (CO-RADS) score on high-resolution computed tomography of the chest, total length of stay in the hospital, and the number of ICU days and ventilator days.Results: We have calculated the mean CT value for all groups and calculated the p-value for statistical significance. For the total length of stay in the hospital and the number of ICU days and ventilator days, we applied the Pearson correlation coefficient.The p-value was statistically significant for mortality, ICU admission, and shock groups. The CT values and the length of ICU stay were inversely correlated with the statistically significant p-value.Conclusion: Low CT value is associated with increased ICU admission, high mortality, shock, and increased length of ICU stay.How to cite this article: Rajyalakshmi B, Samavedam S, Reddy PR, Aluru N. Prognostic Value of “Cycle Threshold” in Confirmed COVID-19 Patients. Indian J Crit Care Med 2021;25(3):322–326.

Experimental characterization of high-energy component in extracted pulsed neutrons at the J-PARC spallation neutron source

This study explores high-energy neutron components of the extracted neutron beam at J-PARC pulsed neutron source using the foil activation method with threshold reactions. Foils of aluminum, gold, bismuth, niobium, and thulium were used to cover the neutron energy range from 0.3 MeV to 79.4 MeV. The experiment was performed using neutron beams of BL10 (NOBORU). The foils were irradiated by a neutron beam at 13.4 m from the moderator. To characterize high-energy neutron fields for irradiation applications, reaction rates in three different configurations with and without B4C slit and Pb filter were examined. To compare the experiments with calculations given for the user, reaction rates for corresponding reactions were calculated by the PHITS code with the JENDL-3.2 cross sections and the JENDL dosimetry file. Although there was a systematic tendency in C/E (Calculation/Experiment) ratios for different threshold energies, which C/E ratio decreased as threshold energy increased up to 100 MeV, all C/E ratios were in the range of 1.0 ± 0.2. This indicated that high-energy neutron calculations were adequate for the analysis of experimental data for NOBORU users.

Peanut allergen reaction thresholds during controlled food challenges in 2 Canadian randomized studies (Canada-ARM1 and PISCES)

Food allergy affects millions worldwide.1 Vigilance by affected individuals and families is necessary to prevent accidental ingestions, allergic reactions, and anaphylaxis. Understanding the minimum amount of food allergen that elicits a reaction—thresholds—in susceptible individuals is paramount to inform safe practice, food manufacturing, and public health policy.1 Thresholds can also inform how to optimize food challenge schedules, advise patients about the potential for accidental reactions, and the design of desensitization approaches.

Using data from food challenges to inform management of consumers with food allergy: A systematic review with individual participant data meta-analysis

BackgroundEliciting doses (EDs) (eg, ED01 or ED05 values, which are the amounts of allergen expected to cause objective symptoms in 1% and 5% of the population with an allergy, respectively) are increasingly being used to inform allergen labeling and clinical management. These values are generated from food challenge, but the frequency of anaphylaxis in response to these low levels of allergen exposure and their reproducibility are unknown.ObjectiveOur aim was to determine (1) the rate of anaphylaxis in response to low-level peanut exposure and (2) the reproducibility of reaction thresholds (and anaphylaxis) at food challenge.MethodsWe conducted a systematic review and individual participant data meta-analysis of studies that reported at least 50 individuals with peanut allergy reacting to peanut at double-blind, placebo-controlled food challenge (DBPCFC) and were published between January 2010 and September 2020. Risk of bias was assessed by using National Institute for Clinical Excellence methodologic checklists.ResultsA total of 19 studies were included (covering a total of 3151 participants, 534 of whom subsequently underwent further peanut challenge). At individual participant data meta-analysis, 4.5% (95% CI, 1.9% to 10.1%) of individuals reacted to 5 mg or less of peanut protein with anaphylaxis (moderate heterogeneity [I2 = 57%]). Intraindividual thresholds varied by up to 3 logs, although this variation was limited to a half-log change in 71.2% (95% CI, 56.2% to 82.6%) of individuals. In all, 2.4% (95% CI, 1.1% to 5.0%) of patients initially tolerated 5 mg of peanut protein but then reacted to this dose at subsequent challenge (low heterogeneity [I2 = 16%]); none developed anaphylaxis.ConclusionAround 5% of individuals reacting to an ED01 or ED05 level of exposure to peanut might develop anaphylaxis in response to that dose. This equates to 1 and 6 anaphylaxis events per 2500 patients exposed to an ED01 or ED05 dose, respectively, in the broader population of individuals with peanut allergy.

The real-time reverse transcription-polymerase chain reaction threshold cycle values for severe acute respiratory syndrome coronavirus 2 predict the prognosis of coronavirus disease 2019 pneumonia.

The clinical course of coronavirus disease 2019 (COVID-19) varies from mild to critical. We retrospectively examined whether clinical and laboratory findings on admission could predict COVID-19 prognosis. Among various factors associated with COVID-19 severity, our results indicated that the real-time reverse transcription-polymerase chain reaction (RT-PCR) threshold cycle (Ct) values for severe acute respiratory syndrome coronavirus 2 were the most useful predictor of COVID-19 prognosis.

Hyperon electromagnetic form factors in the timelike region

Electromagnetic form factors of hyperons ($\Lambda$, $\Sigma$, $\Xi$) in the timelike region, accessible in the reaction $e^+e^- \to \bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $\bar YY$ system. This interaction is taken into account in the calculation, utilizing $\bar YY$ potential models that have been constructed by the J\"ulich group for the analysis of data from the reaction $\bar pp \to \bar YY$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of $e^+e^- \to \bar \Lambda \Lambda$ and $e^+e^- \to \bar \Sigma^0\Lambda$, is reproduced. With regard to the reactions $e^+e^- \to \bar \Sigma^- \Sigma^+, \ \bar\Sigma^0\Sigma^0, \ \bar\Sigma^+\Sigma^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\bar\Sigma\Sigma$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $\Lambda$, $\Sigma$, and $\Xi$ hyperons.

Current Insights into Immunotherapy Approaches for Food Allergy.

In the last decade, there has been increasing research dedicated to food immunotherapy to induce clinical desensitization and provide protection by increasing clinical reaction thresholds. Results from recent food immunotherapy studies with differing routes of administration (oral, sublingual, and epicutaneous) suggest that food immunotherapy can induce clinical desensitization with varying levels of safety, however lasting tolerance has not been demonstrated. Furthermore, treatment side effects and dosing logistics may make the therapies difficult for some supporting the need for alternative treatment approaches. Peptide immunotherapy and DNA vaccine approaches should in theory allow for safer administration by decreasing allergenicity but proof of their clinical efficacy and immunogenicity remains to be proven. Biologic agents may allow for increased safety and rapid up-dosing of immunotherapy with the added benefit of treating multiple allergens simultaneously.

Cross Section of Neutrino Absorption by the Gallium-71 Nucleus

The cross sections of neutrino absorption by the gallium-71 nucleus are obtained for neutrinos from artificial 37Ar, 51Cr, and 65Zn sources. The calculations rely on the new measurement of the energy threshold of this absorption reaction, and contributions of germanium-71 excited states to the total cross section are estimated by invoking the data on the 71Ga(3He,t)71Gе charge-exchange reaction. The results are important for searches for sterile neutrinos in calibration experiments.

Analysis of gas-cooled fast reactor integral shielding experiment: “Wuerenlingen iron benchmark experiment (PROTEUS)” using SuperMC

PROTEUS integral measurement provides one of the rarest fast reactor nuclear systems data with superior accuracy. The PROTEUS reactor is composed of PuO2/UO2 fuel lattice. A detailed 3-D neutronics model and calculation for the PROTEUS facility has been achieved with the SuperMC code. Most of the calculated fission rates for 238U and 239Pu showed an average deviation less than 3% from the measurement. Calculated neutron spectra in both steel-37 and steel-18/8 at the test regions showed a consistent pattern with the experiment; however, it was noticed that there was a systematic underestimation for the higher energy spectrum. The observation was also consistent with the calculated threshold reaction rate: 103Rh (n, n′) 103mRh, 115In (n, n′) In115m, and 32S (n, p) 32P. The majority of the calculated threshold reaction rates were in agreement with experimental values within total uncertainty at 2σ level. The results demonstrate good consistency of the SuperMC for modeling and calculation for reactor analysis.

Predicting driver reaction time and deceleration: Comparison of perception-reaction thresholds and evidence accumulation framework

Prediction of driver reaction to the lead vehicle motion based on the perception-reaction time (PRT) is critical for prediction of rear-end crash risk. This study determines PRT at various spacings in approaching and braking conditions, and examines the association of PRT and deceleration rate with crash risk. For these tasks, a total of 50 drivers’ behavior was observed in a driving simulator experiment with 4 different scenarios – reaction to a decelerating lead vehicle, reaction to a stopped lead vehicle, perception of a lead vehicle’s speed change, and perception of a slow-moving lead vehicle. The study tested three hypotheses of PRT including perception and reaction thresholds and the evidence accumulation framework using a visual variable (tau-inverse). It was found that the drivers neither reacted after a specific PRT from the start of perception nor reacted at a specific value of tau-inverse. Rather, the drivers generally reacted when the accumulation of evidence (tau-inverse) over time reached a threshold. It was also found that the magnitude of deceleration rate depends on the tau-inverse at the start of braking and hence, higher crash risk was associated with higher level of urgency and insufficient brake force rather than longer PRT. This study demonstrates that the evidence accumulation framework is a promising method of predicting driver reaction in approaching and braking conditions for different types of lead vehicle, and the level of urgency is important for predicting the probability of crash.

Cross-sectional study on hearing loss and auditory reaction time before and after spinal anesthesia with marcaine 0.5% in patients undergoing elective surgery

BackgroundHearing loss is a rarely reported complication of spinal anesthesia. The purpose of this study is to assess the effects of 0.5% Maracine (bupivacaine) on hearing threshold and auditory reaction time before and after spinal anesthesia among patients undergoing elective surgery. Materials and methodsThis is a descriptive cross-sectional study performed on 60 patients undergoing elective surgery with ASA Class II and II anesthesia (0.5% bupivacaine) at Khorramabad Nursing Home. After obtaining consent from the patients, audiometry and tympanometry tests were performed using AZ80 and Madsen otoflex tympanometer and related findings including the presence or absence of hearing loss at various frequencies, before and after the surgery, were noted in a form for each patients along with their demographic data. SPSS 21 was used for statistical analysis and the data were analyzed using descriptive statistics and chi-square inferential tests. ResultsAt low frequencies of 250 and 500 Hz, no significant difference in pre- and postoperative hearing threshold in the right ear (P > 0.05) was seen, but at frequencies above 500 Hz, the hearing threshold was significantly decreased after surgery, (P < 0.05). In the left ear at 250, 1000, 3000, and 8000 Hz, there was no significant difference (P > 0.05) between pre- and postoperative hearing threshold. The results of this study showed that the preoperative hearing threshold for men and women did not differ and the auditory threshold and auditory response time after surgery did not differ between the two sexes (P > 0.05). Similarly, the difference was not correlated with the age and the levels of anesthesia (P > 0.05). The results also showed that changes in mean arterial blood pressure (MAP) and heart rate above 30% of baseline were also not correlated with hearing loss (P > 0.05). ConclusionsThe results showed that at certain frequencies, hearing loss was observed in both ears after spinal anesthesia with 5% Marcaine, but this hearing loss was not related to age, sex, and spinal anesthesia level. The results also showed that changes in mean arterial blood pressure (MAP) and heart rate above 30% of baseline did not correlate with hearing loss.

Determination of aluminum in bovine liver SRM 1577c by Instrumental Cold Neutron Activation Analysis

Instrumental neutron activation analysis may need to correct for matrix interferences caused by fast neutron induced threshold reactions. The very low Al mass fraction in bovine liver Standard Reference Material (SRM) has eluded certification due to such complications. Cold neutron beam irradiation absent fast neutrons provides a possible alternative, which has been applied for the first time to determine Al in bovine liver SRM 1577c. The Al mass fraction was determined to be (0.80 ± 0.15) mg/kg using the traditional single peak-fitting method, and (0.78 ± 0.23) mg/kg using a new physics model-based spectral fitting method.

Effect of multi-oxidants on mechanical response and reactive characteristics of PTFE/Al reactive material under dynamic impact

PTFE/Al/Fe2O3, PTFE/Al/MnO2 and PTFE/Al/MoO3 reactive materials specimens were fabricated by referring to the traditional thermite and adding PTFE as matrix. Split Hopkinson pressure bar system tests were carried out to investigate the effect of multi-oxidants on mechanical response and reactive characteristics of PTFE/Al reactive material under dynamic impact. The results show that three oxidants have significant influence on the mechanical behavior and reactive characteristics of the reactive materials. PTFE/Al/Fe2O3 had the highest strength while PTFE/Al/MoO3 exhibited the lowest strength. The reaction time and reaction thresholds of PTFE/Al/Fe2O3, PTFE/Al/MnO2 and PTFE/Al/MoO3 were measured to be 2.5 ms, 2.9 ms, 1.9 ms and 6250 s−1, 5600 s−1, 6500 s−1, respectively. The addition of MnO2 could dramatically improve the explosion intensity, prolong the reaction time and reduce reaction threshold of PTFE/Al reactive material. All the results indicate that MnO2 has great potential for serving as an additive into PTFE/Al system to improve the energy release rate.

Global R-matrix analysis of the 11B(α,n)14N reaction

Reactions that populate the 15N system have implications for nucleosynthesis through the 11B(α, n)14N and 14N(n, p)14C reactions and the 14N(n, p)14C reaction is also a key component in modeling atmospheric 14C production. A convenient characteristic of this system is that the α-particle, proton, and neutron separation energies are all within ≍1 MeV of one another. Further, it has been observed that 11B+α, 14N+n and 14C+p induced reactions all populate many of the same resonances near their reaction thresholds. This strongly facilitates the simultaneous analysis of data for all three of these entrance partitions using a global R-matrix analysis, which in turn provides a method of comparing the consistency among the different experimental measurements. In this work, a new measurement has been performed for the 11B(α, n)14N reaction, which gives a more accurate description of the cross section, in particular over an important interference region. This new data is combined with results from previous measurements, which populate a similar excitation energy range in the 15N system, to produce a global fit that includes 11B(α, n)14N reaction data for the first time.

SARS-CoV-2 screening of asymptomatic women admitted for delivery must be performed with a combination of microbiological techniques: an observational study.

ABSTRACTIntroductionThe aim of this study is to assess the value of systematic screening in asymptomatic women admitted for spontaneous delivery with a combination of reverse transcription polymerase chain reaction (RT-PCR) and cycle threshold (Ct) and serum antibodies.Material and methodsSince May 6 all women admitted for spontaneous delivery underwent RT-PCR in nasopharyngeal swabs and specific antibodies IgG of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in serum that were performed as part of routine clinical care in our institution. Ct of the PCR was recorded. We analyzed the first 100 women consecutively admitted for spontaneous delivery at our institution.ResultsNine women were positive for SARS-CoV-2 in nasopharyngeal samples (9%) and 13 (13%) presented positive specific antibodies of the coronavirus. Overall, SAR-CoV-2 prior exposure was 15%. The Ct determination (RT-PCR test) of our 9 positive patients ranged from 36 to 41 cycles with a median of 40. Vaginal delivery occurred in 94% of the cases and only 6% underwent a cesarean section, always for obstetric reasons. No fetal transmission was observed and maternal and neonatal prognosis was excellent.ConclusionsDuring epidemic episodes in asymptomatic women in labor, universal testing with RT-PCR (considering Ct determination), and the detection of antibodies, permits a better interpretation of the results and avoid unnecessary isolation procedures.

Cross sections of 56Fe(n, p)56Mn, 55Mn(n, p)55Cr, 52Cr(n, p)52V, 56Fe(n, α)53Cr, 55Mn(n, α)52V and 52Cr(n, α)49Ti reactions using phenomenological level density models from threshold to 20 MeV

56Fe(n,p)56Mn, 55Mn(n,p)55Cr, 52Cr(n,p)52V, 56Fe(n, α)53Cr, 55Mn(n, α)52V and 52Cr(n, α)49Ti reactions are evaluated using four phenomenological nuclear level density models from reaction threshold to 20 MeV. The calculated data is compared with the experimental nuclear reaction data from EXFOR database. Statistical factors H, D and R are computed to identify the best fit. Level density parameters are adjusted for further improvement of the fitting. Back shifted Farmi-gas model gives a resemblance of neutron-induced 56Fe, 55Mn and constant temperature Fermi-gas model gives a closeness for 52Cr reaction with our new parameter values.

Experimental study of the Ho165(n,2n) reaction: Cross section measurements for the population of the Ho164 ground state and isomeric state from the threshold up to 20 MeV

In the present work the $^{165}\mathrm{Ho}(n,2n)$ reaction was studied experimentally and theoretically for the population of the ground state (${J}^{\ensuremath{\pi}}={1}^{+}$) of the $^{164}\mathrm{Ho}$ product nucleus, as well as for the population of its isomeric state (${E}_{ex}=139.8$ keV, ${J}^{\ensuremath{\pi}}={6}^{\ensuremath{-}}$). The cross sections of both the ground and isomeric state channels were measured at energies near the reaction threshold (${E}_{th}=8.04$ MeV), at 10.1, 10.4, and 10.7 MeV, as well as at energies higher than 17 MeV, at 17.1, 18.1, 19.0, and 19.6 MeV. The adopted method was the activation technique relative to the $^{197}\mathrm{Au}(n,2n)^{196}\mathrm{Au}$ and $^{27}\mathrm{Al}(n,\ensuremath{\alpha})^{24}\mathrm{Na}$ reference reactions. The quasi-monoenergetic neutron beams for the near threshold energies were produced via the $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$ reaction, while for the neutron beams above 17 MeV the $^{3}\mathrm{H}(d,n)^{4}\mathrm{He}$ reaction was utilized. In both cases the deuteron beams were delivered by the 5.5 MV Tandem Van de Graaff accelerator of the Institute of Nuclear and Particle Physics at N.C.S.R. ``Demokritos''. Additional to the experimental study, calculations were performed using the talys code (v. 1.9). The experimental data of the present work along with the previous measurements were compared with the talys results so as to investigate the reproduction of the experimental data for the different level density models of the code.

Combustion and emission behavior of different waste fuel blends in a laboratory furnace

The paper discusses the results of lab-scale combustion of complex waste-derived fuel mixtures in different forms. Composite fuels based on a combination of widespread industrial and municipal waste were considered. The scientific and practical novelty of this study comes from the fact that for the first time, a group of integral parameters was researched. They describe the ignition and combustion of mixtures in different forms: pressed dry fuel (pellets), a wet slurry, and granules of different moisture content. The most efficient method in terms of increasing the rate and reducing the temperature threshold of the oxidation reaction is firing a low-moisture mixture based on municipal solid waste (with a predominance of wood components). Pelleted coal sludge combustion was characterized by a rather long delay in heterogeneous ignition and underburning. It was shown that in order to reduce emissions and increase the degree of burnout, coal processing waste should be burned as wet granules or slurry droplets.

Oral food challenges.

Oral food challenge (OFC) is a procedure that is conducted most commonly by allergist/immunologists in their office or in food allergy centers to confirm a food allergy or to confirm tolerance to the food. The procedure as conducted in clinical practice is mostly open food challenge and, in research, a double-blind, placebo controlled food challenge. OFC has associated risks that can be minimized by having the challenges conducted by trained personnel who are prepared to treat allergic reactions and who have rescue medications available. However, OFCs have tremendous benefits to the patients and their families, including the potential to determine that a food is no longer an allergen and can be introduced into the diet. Even OFCs that result in clinical reactions have the benefit of confirming the food allergy and demonstrating the therapeutic effect of the rescue medications. The study of the outcomes of OFC has shed light on food allergy reactions and characteristics of the patients with food allergy as well as on the value of other diagnostic tests compared with OFC. OFCs have helped establish food allergy thresholds, confirm that subjects enrolled in research studies have the allergy, and demonstrate the response to the therapies tested in terms of ameliorating the allergic response or raising the reaction threshold. OFCs have also been used to promote the recent guidelines for the prevention of peanut allergy by identifying the infants at risk for peanut allergy but who are not allergic yet.