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1.
Curr Sports Med Rep ; 20(10): 518-519, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34622815

RESUMO

ABSTRACT: The spontaneous regression of an osteochondroma is extremely rare. We report a case of medial femoral condyle impaction fracture over the site of spontaneous regression of a pedunculated osteochondroma discovered on advanced imaging after an acute injury in a 16-year-old male American football athlete. Although spontaneous regression of an osteochondroma has been described, the case presented reveals questions regarding resultant architectural changes to the bone after resorption, leaving it prone to injury. This is the first case that describes increased injury risk potential at the site of osteochondral regression.

2.
Phys Sportsmed ; : 1-4, 2021 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-34346850

RESUMO

OBJECTIVE: Hallux sesamoid injuries are well described and can be debilitating and chronically disabling. The role of orthobiologics such as platelet-rich plasma (PRP) in sesamoid injuries has not been reported. This study describes three cases of recalcitrant hallux sesamoid injuries in teenage athletes who returned to impact activities, pain free, following one treatment of PRP. METHODS: This is a case-series study describing three teenage athletes presenting to a tertiary level pediatric sports medicine practice with chronic hallux sesamoid injuries. RESULTS: The three patients (two female, one male) described in this case series were 13-, 16-, and 17-year-old athletes. Their primary sports were ballet, basketball, and Irish step dance, respectively. All three athletes received PRP: two received unilateral treatment (one tibial sesamoid, one fibular sesamoid) and one received treatment to bilateral tibial sesamoids. The average duration of symptoms prior to PRP was 52.5 weeks (14-128 weeks). The average time out of their primary sport was 48.7 weeks (20-78 weeks). Three of the 4 sesamoids treated with PRP were tibial sesamoids. Each site of injury was treated with one treatment of leukocyte-rich PRP. All three athletes were cleared to return to impact activities such as running and jumping at 6-9 weeks following PRP, specifically 9 weeks after the final PRP injection for the patient who underwent bilateral treatments. CONCLUSION: In the three cases provided of sesamoid injuries treated with PRP, the time to return to impact activities was less than reported for athletes not treated with PRP. Acknowledging that other management factors likely contributed to return to impact activities, this case series sets the groundwork for future research investigating the role of PRP with needle fenestration in the treatment of sesamoid injuries.

3.
Am J Cardiol ; 152: 146-149, 2021 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-34237610

RESUMO

The optimal screening strategy to prevent sudden cardiac death (SCD) in athletes remains unknown. Pre-participation screening with electrocardiogram (ECG) remains controversial. The utility and accuracy of limb-lead (LL) ECG alone in identifying cardiac abnormalities associated with SCD has not been studied. This study was a comparative secondary data analysis, comparing the interpretation accuracy of 4 physicians evaluating publicly available ECGs of the most common cardiac conditions associated with SCD in athletes. Each physician interpreted a total of 100 ECGs: 50 normal ECGs (25 LL and 25 standard 12L) and 50 abnormal ECGs (25 LL and 25 standard 12L). The agreement between LL ECGs and 12L ECGs was assessed by Cohen's kappa coefficient and the accuracy of identifying an abnormal ECG was compared across LL and 12L ECGs using a chi-squared test. Inter-rater reliability was assessed by estimating the Fleiss's kappa coefficient. The sensitivity of LL ECG and 12L ECG was identical at 86%. The specificity of LL ECG was 75% (95% CI = 65% to 83%) and 12L ECG was 82% (95% CI = 73% to 89%). Substantial agreement was seen between LL ECG and 12L ECG interpretation across all readers (k = 0.63; 95% CI = 0.49 to 0.77). Interpretation accuracy was 81% (95% CI = 74% to 86%) and 84% (95% CI 78% to 89%) using LL ECG and 12L ECG, respectively (p = 0.43). In conclusion, the accuracy, sensitivity, and specificity were high and comparable for both LL ECG and 12L ECG in identifying cardiovascular conditions associated with SCD. Agreement between LL ECG and 12L ECG was substantial.


Assuntos
Atletas , Doenças Cardiovasculares/diagnóstico , Morte Súbita Cardíaca/prevenção & controle , Eletrocardiografia/métodos , Displasia Arritmogênica Ventricular Direita/complicações , Displasia Arritmogênica Ventricular Direita/diagnóstico , Displasia Arritmogênica Ventricular Direita/fisiopatologia , Síndrome de Brugada/complicações , Síndrome de Brugada/diagnóstico , Síndrome de Brugada/fisiopatologia , Cardiomiopatia Dilatada/complicações , Cardiomiopatia Dilatada/diagnóstico , Cardiomiopatia Dilatada/fisiopatologia , Cardiomiopatia Hipertrófica/complicações , Cardiomiopatia Hipertrófica/diagnóstico , Cardiomiopatia Hipertrófica/fisiopatologia , Doenças Cardiovasculares/complicações , Doenças Cardiovasculares/fisiopatologia , Morte Súbita Cardíaca/etiologia , Humanos , Síndrome do QT Longo/complicações , Síndrome do QT Longo/diagnóstico , Síndrome do QT Longo/fisiopatologia , Programas de Rastreamento , Miocardite/complicações , Miocardite/diagnóstico , Miocardite/fisiopatologia , Síndrome de Wolff-Parkinson-White/complicações , Síndrome de Wolff-Parkinson-White/diagnóstico , Síndrome de Wolff-Parkinson-White/fisiopatologia
4.
Dalton Trans ; 50(26): 9259-9268, 2021 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-34128517

RESUMO

Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(ii) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H2O as products. After the initial H-atom abstraction step, two different reaction pathways have been identified that are distinguished by the participation of alkyl hydroperoxide (referred to as the "open" cycle) versus the methanol side-product (referred to as the "closed" cycle) within the catalyst recovery process. Importantly, both pathways involve dehydrogenation and re-hydrogenation of the -NH2 group bound to the Cu-site - a feature that is revealed from the ensemble sampling of configurations of the reactive species that are stabilized within the explicit solvent environment of the simulation. Estimation of the energy span from the experimental turnover frequency yields an approximate value of 22.7 kcal mol-1 at 350 K. Whereas the closed cycle value is predicted to be 26.2 kcal mol-1, the open cycle value at 16.5 kcal mol-1. Both pathways are further consistent with the equilibrium between Cu(ii) and Cu(iii) that has previously been observed. In comparison to prior static DFT calculations, the ensemble of both solute and solvent configurations has helped to reveal a breadth of processes that underpin the full catalytic cycle yielding a more comprehensive understanding of the importance of radical reactions and catalysis recovery.

5.
J Comput Chem ; 42(19): 1344-1353, 2021 07 15.
Artigo em Inglês | MEDLINE | ID: mdl-33977539

RESUMO

The two dissociation channels of HOOH, namely, HOOH and HOOH, in water and methanol are investigated using umbrella-sampling ab initio molecular dynamics. Our potential of mean force calculations reveals the HOOH dissociation to be more favorable in methanol with a free energy barrier of 7.56 kcal/mol, while the HOOH dissociation possesses a free energy barrier of 11.46 kcal/mol. In water, the HOOH dissociation channel is more favorable (8.25 kcal/mol), while the HOOH dissociation process requires a higher free energy (11.28 kcal/mol). Such reaction favorability can be explained by inspecting the formation of secondary radical species during the course of multiple hydrogen donating-accepting processes in each reaction channel. The radical species, that is, H3 O• (observed in water) and CH3 OH2 • (observed in methanol), are the first subordinate species upon the HOOH dissociation. For the HOOH dissociation channel in methanol, the secondary species such as water and formaldehyde can be observed, while the re-generation of HOOH in water can be spotted.

6.
Curr Sports Med Rep ; 20(2): 109-112, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-33560035

RESUMO

ABSTRACT: The availability of handheld ultrasound offers physicians an opportunity to better define anatomy and pathophysiology, thus enhancing the diagnostic capabilities of a standard physical examination. The medical community increasingly embraces the potential for point-of-care ultrasound across medical specialties. The primary aim of this review was to identify and compile information on the current clinical utility of point-of-care ultrasound for musculoskeletal examination. This information will enable health care providers to understand the current utility and potential of musculoskeletal point-of-care ultrasound, thus facilitating its appropriate adoption into clinical practice.


Assuntos
Sistema Musculoesquelético/diagnóstico por imagem , Sistema Musculoesquelético/lesões , Exame Físico/métodos , Testes Imediatos , Traumatismos em Atletas/diagnóstico por imagem , Humanos , Ultrassonografia
7.
Phys Chem Chem Phys ; 22(32): 18149-18154, 2020 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-32766624

RESUMO

The reaction probability and kinetics of the water splitting process on the penta-NiAs2 monolayer are studied using ab initio molecular dynamics simulations. A total of 100 trajectories are investigated, in which a H2O molecule is set to strike the surface with a translational energy of 1 eV or 2 eV. The results show that the NiAs2 monolayer is an excellent candidate for the activation of water splitting with a reaction probability of 94% for both energy levels. Interestingly, the kinetics of two O-H dissociation stages varies greatly with respect to the inletting translational energy. Interpreting the reaction data for the 1 eV case, we conclude that O-H1 and O-H2 dissociations are first-order processes. However, such dissociation steps become pseudo-zeroth order in the 2 eV case. At the time of the dissociation, the force acting on atoms and the principal component analysis suggest that the two OH breaking stages behave like harmonic springs until reaching the dissociation.

8.
ACS Omega ; 5(26): 16139-16148, 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32656436

RESUMO

The source of induced magnetism in the MoS2 monolayer induced by transition metal (Fe/Ni) collision is investigated using nonadiabatic ab inito molecular dynamics simulations that take into account high-spin and low-spin energy states during trajectory integration. By considering various metal firing angles, a strong interaction between the Fe/Ni atom and the MoS2 surface can be observed because of enormous increase in the kinetic energy of the metal atom. When firing along the Mo-S bond, the Fe bullet is pulled more strongly than when firing along the S-Mo-S bisector. Spin polarization of MoS2 is gradually induced when Fe approaches the surface and eliminated when Fe roams around a potential energy trap on the MoS2 layer. We observe that there is charge transfer between Fe and Mo atoms, which enhances the probability of electron pairing and leads to instantaneous vanishing of total magnetization. The Ni-MoS2 system is found to establish a total magnetization of 1.5-4 µB when Ni is 2.0 Å above the surface. Interestingly, the strong bonding attachment of Ni suppresses the band gap to at least 40%.

9.
J Sports Med Phys Fitness ; 60(10): 1412-1414, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32586080

RESUMO

There are many causes of acute hip pain. Obturator internus (OI) muscle strain is a rare cause of the presentation. We report a case of OI muscle strain in a 15-year-old ski racer who presented with new onset acute right hip pain. Magnetic resonance imaging showed enhancement of the obturator internus muscle indicating muscle injury. Patient was treated conservatively with target physical therapy and NSAIDs for pain management. This case illustrates an atypical diagnosis for a common chief complaint.


Assuntos
Músculo Esquelético/lesões , Esqui/lesões , Entorses e Distensões/diagnóstico por imagem , Adolescente , Artralgia/etiologia , Articulação do Quadril/diagnóstico por imagem , Humanos , Imageamento por Ressonância Magnética , Masculino , Músculo Esquelético/diagnóstico por imagem , Modalidades de Fisioterapia , Entorses e Distensões/terapia
10.
Phys Chem Chem Phys ; 21(34): 18605-18611, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31414089

RESUMO

In this study, we revisit the proton transfer mechanism in [Zn(HPO4)(H2PO4)]2-, a coordination polymer possessing high proton conductivity. In a previous report [N. Phattharasupakun, J. Wutthiprom, S. Kaenket, Th. Maihom, J. Limtrakul, M. Probst, S. S. Nagarkar, S. Horike and M. Sawangphruk, Chem. Commun., 2017, 53, 11786-11789], it was hypothesized that protons could move along the ImH+ chain involving phosphate anions within the polymer structure, with energy barriers >1.3 eV. Adopting M06-2X calculations to examine the reaction pathway, we observe that it is much more favorable for H+ to move along a one-dimensional channel formed by HPO42- and H2PO4- anions. Within a unit cell, the proton hopping process can be divided into three elementary steps. For the forward proton transfer direction, the maximum energy barrier is only 0.04 eV, while that of the backward direction is 0.27 eV. Even though the barriers of the backward direction seem to outreach the barriers of the forward direction, both are still low in comparison with those reported in the literature. Moreover, we also point out the involvement of PO4 rotation during the proton transfer process. Activation energies of 0.37 eV and 0.15 eV are required for single steps of rotation of the phosphate anion. Both H+ translation (hopping) and rotation steps of PO4 anions simultaneously participate in the course of proton transfer in the coordination polymer.

11.
Sci Rep ; 8(1): 16651, 2018 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-30413771

RESUMO

In this study, we conduct a density functional theory investigation to study the mechanical stability of a titanium-based metal organic framework (MOF-901), which was hypothetically assumed to possess 2D characteristics. It is systematically found that the encapsulation of methanol enhances the mechanical stability of MOF-901 as the elastic tensors Cij of MOF-901∙nMeOH are higher than the corresponding Cij quantities reported for solvent-free MOF-901. Moreover, the 2D characteristics of MOF-901 is confirmed by verifying the negative values of C33. At the same time, the band gap of MOF-901 is observed to be solvent-dependent. In its pure form, MOF-901 possesses a direct gap (Eg) of 2.07 eV, with the valence and conduction bands mainly constituted by electrons of 4-aminobenzoate linkers. Introducing methanol into MOF-901 causes distortion to the 4-aminobenzoate geometry, thereby induces electronic degeneracy to the conduction bands. Consequently, Eg is narrowed to 1.84 eV with 5.7 wt% MeOH or 1.63 eV with 11.4 wt% MeOH. Hence, it is possible to tailor the band gap of MOF-901 by controlling methanol guest, which only acquires van der Waals interaction to the framework. In addition, our theoretical prediction shows a Ti(IV) site can undergo electronic hopping to become Ti(III) under the effect of visible light (~440-443 nm). Then, Ti(III) is capable of breaking the C-Br bond in ethyl α-bromophenylacetate spontaneously, which in turn activates the polymerization of methyl methacrylate with an energy barrier of 0.30 eV.

12.
Phys Chem Chem Phys ; 20(41): 26786, 2018 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-30306989

RESUMO

Correction for 'Penetrating probability and cross section of the Li+-C60 encapsulation process through an ab initio molecular dynamics investigation' by Thi H. Ho et al., Phys. Chem. Chem. Phys., 2018, 20, 7007-7013.

13.
Phys Chem Chem Phys ; 20(10): 7007-7013, 2018 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-29468229

RESUMO

The endohedral complex system of Li+-C60 has been shown to possess interesting applications in photovoltaics, supramolecular chemistry, and functionalized materials. In this study, we perform a theoretical investigation of Li+ encapsulation within a C60 cage by employing an ab initio molecular dynamics approach. The Li+ cation is positioned 9 Å away from the C60 center of mass, and fired towards a randomized spot in a six-membered ring with a certain level of inletting energy, which is 7.5 eV, 9 eV, 12 eV, or 15 eV. In total, 2000 samples of MD trajectories are investigated. Our statistical results yielded a penetrating probability in the range of 0.8% to 15.6% with respect to the above inletting energy, while the cross section ranges from 0.006 Å2 to 0.123 Å2. Moreover, we observed that the penetrating probability exhibited direct proportionality to the inletting energy. Hence, we can determine that the minimum required inletting energy for reaction occurrence is 6.6 eV. Overall, it seems difficult for Li+ to penetrate through the sp2-carbon wall, because a very high inletting energy is required to open the entrance. At the same time, Li+ must approach closely to the center of a six-membered ring to enhance the penetration probability.

14.
Phys Chem Chem Phys ; 19(40): 27332-27342, 2017 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-28971193

RESUMO

We present in this study a theoretical investigation of the collision of Li with the MX2 surface (MoSe2 or WS2) by employing the Born-Oppenheimer molecular dynamics (MD) approach. In each trajectory, atomic Li is fired toward the two-dimensional monolayer with an inletting kinetic energy of 0.2 eV or 2.0 eV and a chosen striking angle. In total, 84 MD trajectories are analyzed. We observe that Li has a high tendency to migrate on WS2 in most investigated cases (20/21 cases at 0.2 eV inletting kinetic energy and 21/21 cases at 2.0 eV inletting kinetic energy), while the migration probability on MoSe2 is much lower (only 5/21 cases with the inletting kinetic energy of 0.2 eV and 15/21 cases with the inletting kinetic energy of 2.0 eV). Interestingly, our finding shows that the migration probability does not depend on the binding energies of Li-MoSe2 (1.61 eV) and Li-WS2 (1.77 eV), but it is in good agreement with the nudged-elastic-band prediction of migration barriers. In fact, it is the intensity of elastic vibration of the transition metal dichalcogenide layer that plays a very significant role in the migration of Li. During the collision process, Li is able to absorb energy from the layer vibration to jump out from one X-X-X trap to another. Consequently, with the assistance from intensive vibration of WS2, Li would possess higher migration probability on the layer surface. Finally, electronic structure analysis on various interacting Li-MX2 configurations is performed. From Bader charge estimation, we observe that WS2 tends to establish more charge transferability with Li. Moreover, when Li approaches closer to the S/Se layer, the hybridization of Li-2s and Mo-4d (or W-5d) orbitals results in a magnetic moment (up to ∼1 µB).

15.
Chemphyschem ; 18(10): 1376-1384, 2017 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-28181722

RESUMO

In this study, we examine the adsorptions of Ni, Pd, and Pt clusters on C60 by using a computational approach. Our calculation results show that the base structure of C60 can host Nin /Pdn /Ptn (n=1-4) clusters with good adsorption stability and the complexes establish either two or no unpaired electrons. The binding energy of Pd and Pt clusters increases as the number of metal atoms increases, implying that the coverage of C60 with Pd or Pt preferentially establishes a large-size metal cluster. A single metal atom favorably occupies the C-C bridge site. For dimer clusters, the three metals of interest share a similar binding fashion, in which two metal atoms establish direct interactions with the C-C bridge sites. For trimer adsorptions, the formation of linear and triangular structures is observed. Both Pt3 and Ni3 preferably constitute isosceles triangles on C60 , whilst Pd3 favorably establishes a linear shape. Finally, for each of the Ni4 and Pd4 adsorption cases, we observed three stable binding configurations: rhombus, tetrahedron, and Y-form. Whereas Ni4 establishes a tetrahedral form, Pd4 attains the most stable form with the Y-shape geometry on C60 . Overall, we observe that the trend of Pd binding to C60 tends to go beyond the fashion of Ni and Pt. In terms of magnetic alignment, the Pdn -C60 systems seem to be non-magnetic in most cases, unlike the Ni and Pt cases, the structures of which possess magnetic moments of 2 µB in their most stable forms.

16.
Am J Health Syst Pharm ; 74(8): 599-604, 2017 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-28235868

RESUMO

PURPOSE: Results of a study of stress and negative affect levels in postgraduate year 1 (PGY1) and postgraduate year 2 (PGY2) pharmacy residents are presented. METHODS: A cross-sectional approach was used. Pharmacy residency program directors received e-mailed invitation letters requesting that they ask their residents to participate in an online survey in 2011. The main study outcomes included evaluation of resident scores on the 10-item Perceived Stress Scale (PSS10) and the Multiple Affect Adjective Checklist-Revised (MAACL-R) anxiety, depression, hostility, and dysphoria subscales. RESULTS: Of the 524 pharmacy residents included in the study, 75.4% were female, 41.2% were under 26 years of age, and 41% reported working more than 60 hours per week. There were no significant differences between PGY1 and PGY2 residents in stress levels, as assessed with the PSS10 (mean ± S.D. score, 19.05 ± 5.96 versus 19.09 ± 5.77). MAACL-R scores for hostility were, on average, higher among PGY2 residents (mean ± S.D., 50.83 ± 10.02) than among PGY1 residents (48.62 ± 8.96), while there were no significant differences in anxiety, depression, and dysphoria levels. Relative to residents who worked 60 or fewer hours per week, those who worked more than 60 hours had higher perceived stress levels as well as higher depression, hostility, and dysphoria scores. CONCLUSION: Pharmacy residents exhibited high levels of perceived stress, especially those who worked more than 60 hours per week. Perceived stress was highly correlated to negative affect levels.


Assuntos
Estresse Ocupacional/epidemiologia , Assistência Farmacêutica/estatística & dados numéricos , Residências em Farmácia/estatística & dados numéricos , Adulto , Ansiedade/epidemiologia , Ansiedade/psicologia , Estudos Transversais , Depressão/epidemiologia , Depressão/psicologia , Educação de Pós-Graduação em Farmácia , Feminino , Humanos , Masculino , Estresse Ocupacional/psicologia , Inquéritos e Questionários/estatística & dados numéricos , Fatores de Tempo , Tolerância ao Trabalho Programado/psicologia , Adulto Jovem
17.
J Phys Condens Matter ; 29(1): 015003, 2017 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-27830656

RESUMO

In this paper, we propose the use of benzene (Bz) to cover the active site on top of a transition metal atom (Cr/Mn/Fe) adsorbed on the MoS2 monolayer. Stable configurations of adatom on the MoS2 surface were predicted using first-principles calculations and their electronic, magnetic properties were investigated. In addition, the influence of vertical electric field on the electronic band structures of the systems was carefully examined. Analyzing the adsorption energies of transition metals given by the PBE calculations, we found that the benzene molecule stabilized the binding of Cr and Mn on the MoS2 surface, but destabilized the Fe binding by approximately 33% of adsorption energy. The attachment of benzene caused modifications on the total magnetizations of the Cr-MoS2 and Mn-MoS2 structures. The Bz-Mn@MoS2 structure was found to exhibit half-metallicity with 100% spin polarization at the Fermi level. The influence of various degrees of vertical electric field was shown to produce a tensile stress, which altered the lattice parameters and led to band gap narrowing and dramatic shifts of the Fermi level.

18.
J Phys Condens Matter ; 28(13): 135301, 2016 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-26940978

RESUMO

By employing DFT + U calculations with the linear response method, we investigate the interactions between various 3d transition-metal atoms (Cr, Mn, Fe, Co) and silicene. In the cases of two-dimensional (2D) FeSi2 and CoSi2, the metal atoms tend to penetrate into the silicene layer. While CoSi2 is non-magnetic, FeSi2 exhibits a total magnetic moment of 2.21 µ(B)/cell. Upon the examination of 2D MSi6, a trend in anti-ferromagnetic (AFM) favorability in the z-direction is observed according to our DFT + U calculations. In the ferromagnetic (FM) states (less stable), each primary unit cell of CrSi6, MnSi6, and FeSi6 possesses different levels of total magnetization (4.01, 5.18, and 2.00 µ B/cell, respectively). The absolute magnetization given by AFM MSi6 structures varies in the range of 5.33-5.84 µ(B)/cell. A direct band gap in AFM MnSi6 (0.2 eV) is predicted, while the metastable FM FeSi6 structure has a wider band gap (0.85 eV). Interestingly, there are superexchange interactions between metal atoms in the MSi6 systems, which result in the AFM alignments.

19.
J Phys Chem A ; 120(3): 346-55, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26741404

RESUMO

The dissociation dynamics of the O-H bond in Al-OH2 is investigated on an approximated ab initio potential energy surface (PES). By adopting a dynamic sampling method, we obtain a database of 92 834 configurations. The potential energy for each point is calculated using MP2/6-311G (3df, 2p) calculations; then, a 60-neuron feed-forward neural network is utilized to fit the data to construct an analytic PES. The root-mean-square error (rmse) for the training set is reported as 0.0036 eV, while the rmse for the independent testing set is 0.0034 eV. Such excellent fitting accuracy indeed confirms the reliability of the constructed PES. Subsequently, quasi-classical molecular dynamics (MD) trajectories are performed on the constructed PES at various levels of vibrational excitation in the range of 1.03 to 2.23 eV to investigate the probability of O-H bond dissociation. The results indicate a linear relationship between reaction probability and internal energy, from which we can determine the minimum activation internal energy required for the dissociation as 0.62 eV. Moreover, the O-H bond rupture is shown to be highly correlated with the formation of Al-O bond.

20.
J Phys Condens Matter ; 27(30): 305005, 2015 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-26173094

RESUMO

Using first-principles calculations, we investigate the interactions between a WS2 monolayer and several gas molecules (CO, H2O, NO, and O2). Different sets of calculations are performed based on generalized-gradient approximations (GGAs) and GGA + U ([Formula: see text] eV) calculations with D2 dispersion corrections. In general, GGA and GGA + U establish good consistency with each other in terms of absorption stability and band gap estimations. Van der Waals density functional (vdW-DF) calculations are also performed to validate long-range gas molecule-WS2 monolayer interactions, and the resultant absorption energies of four gas-absorption cases (from 0.21 to 0.25 eV) are significantly larger than those obtained from calculations using empirical D2 corrections (from 0.11 to 0.19 eV). The reported absorption energies clearly indicate van der Waals interactions between the WS2 monolayer and gas molecules. The NO and O2 absorptions are shown to narrow the band gaps of the WS2 material to 0.75-0.95 eV and produce small magnetic moments (0.71 µB and 1.62 µB, respectively). Moreover, these two gas molecules also possess good charge transferability to WS2. This observation is important for NO- and O2-sensing applications on the WS2 surface. Interestingly, WS2 can also activate the dissociation of O2 with an estimated barrier of 2.23 eV.

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