558 research outputs found
Soft computing approach for prediction of surface settlement induced by earth pressure balance shield tunneling
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A novel layer-structured PtN₂: first-principles calculations
Platinum nitride as the first successfully synthesized noble metal nitride shows superior mechanical properties and exotic electronic structure that rival those of conventional transition metal nitrides. In the past diverse crystal structures have been proposed to understand its unusual properties. However, very few works pay attention to the dynamic stability of these phases. Here, we examine the potential structures of platinum nitride with a chemical composition of PtN₂ by utilizing a widely adopted evolutionary methodology for crystal structure prediction. Except reproducing the previously proposed phases, we also identify a Pmmm symmetric novel layer structure with a low formation enthalpy that is slightly lower than those of marcasite and CoSb₂ structures but slightly higher than that of pyrite structure. The elastic constants and the lattice dynamical calculations show that this layer-structured PtN₂ is mechanically and dynamically stable. The calculated band structures suggest this new phase together with the simple tetragonal phase are metallic, while other phases are insulators. In addition, it is found that the fluorite structure is dynamically unstable by the phonon spectrum calculations, although it is mechanically stable as suggested by calculated elastic constants.Розглянуто потенційні структури нітриду платини з хімічним складом PtN₂, використовуючи широко прийняту еволюційну методологію прогнозування кристалічних структур. Крім відтворення раніше запропонованих фаз, ідентифіковано нову симетричну шарувату структуру, просторова група Pmmm, з низькою ентальпією формування, яка трохи менша, ніж ентальпії структур марказиту і CoSb₂, але дещо більша, ніж ентальпія структури піриту. Постійні пружності і динамічні розрахунки решітки показують, що цей нітрид платини (PtN₂) з шаруватою структурою механічно і динамічно стабільний. Розраховані зонні структури дозволяють припустити, що ця нова фаза разом з простою тетрагональною фазою є металічною, тоді як інші фази є діелектричні. Розрахунками фононного спектру встановлено, що структура флюориту динамічно нестабільна, хоча механічно стабільна, як передбачається розрахованими константами пружності.Рассмотрены потенциальные структуры нитрида платины с химическим составом PtN₂, используя широко принятую эволюционную методологию прогнозирования кристаллических структур. Кроме воспроизведения ранее предложенных фаз, идентифировано новую симметричную слоистую структуру, пространственная группа Pmmm, с низкой энтальпией формирования, которая немного меньше, чем энтальпии структур марказита и CoSb₂, но немного больше, чем энтальпия структуры пирита. Постоянные упругости и динамические расчеты решетки показывают, что этот нитрид платины (PtN₂) со слоистой структурой механически и динамически стабилен. Рассчитанные зонные структуры позволяют предположить, что эта новая фаза вместе с простой тетрагональной фазой является металлической, тогда как другие фазы являются диэлектрическими. Расчетами фононного спектра установлено, что структура флюорита динамически нестабильна, хотя механически стабильна, как предполагается рассчитанными константами упругости
Associative effects in diets composed of alfalfa and corn soybean concentrate fed to growing cashmere goats
The associative effects resulting from the proportions of neutral detergent fibre (NDF) and non fibre carbohydrate (NFC) were explored and assessed by in vitro gas production . Total mixed rations (TMR) composed primarily of alf a lfa and corn soybean concentrate were fed to growing cashmere goats. Treatments were defined by three proportions of NFC and NDF namely 2.00 ( TMR1), 2.35 ( TMR2), and 3.00 ( that were used to grow cashmere goats , and these TRMs were incubated for 48 h ours to evaluate their influence on associative effects. The results indicated that the associative influences of these treatments on gas production occurred within the cultures predominantly at 2 8 hours, and disappeared gradually as culture time was ex tended . TMR 2 and TMR3 incubation increased gas production compared with that observed in the other groups at all incubation times P > 0.05), and these groups exhibited positive associative effects, particularly during the early hours of incubation P <0.05 )). TMR 3 displayed the best associative effect
Dynamics near the Surface Reconstruction of W(100)
Using Brownian molecular dynamics simulation, we study the surface dynamics
near the reconstruction transition of W(100) via a model Hamiltonian. Results
for the softening and broadening of the surface phonon spectrum near the
transition are compared with previous calculations and with He atom scattering
data. From the critical behavior of the central peak in the dynamical structure
factor, we also estimate the exponent of the power law anomaly for adatom
diffusion near the transition temperature.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
The interference between virtual photon and 1-- charmonium in e+e-experiment
e+e- Experiments producing charmonium are reviewed. It is found that the
contribution of the continuum amplitude via virtual photon was neglected in
almost all the experiments and the channels analyzed. It is shown that the
contribution of the continuum part may affect the final results significantly
in psi(2S) and psi(3770) decays, while the interference between continuum and
resonance amplitudes may even affect the J/psi decays as well as the psi(2S)
and psi(3770). This should be considered in analyzing the "rho-pi puzzle"
between J/psi and psi(2s) decays, and the difference between inclusive hadron
and DDbar cross sections in psi(3770) decays.Comment: 6 pages, 2 figure
Large scale quantum simulations: C_60 impacts on a semiconducting surface
We present tight binding molecular dynamics simulations of C_60 collisions on
the reconstructed diamond(111) surface, carried out with an O(N) method and
with cells containing 1140 atoms. The results of our simulations are in very
good agreement with experiments performed under the same impact conditions.
Furthermore our calculations provide a detailed characterization of the
microscopic processes occuring during the collision, and allow the
identification of three impact regimes, as a function of the fullerene incident
energy. Finally, the study of the reactivity between the cluster and the
surface gives insight into the deposition mechanisms of C_60 on semiconducting
substrates
Ganoderma lucidum extract inhibits proliferation of SW 480 human colorectal cancer cells
Aim: Ganoderma lucidum is a commonly used Chinese herb and an important ingredient in traditional Chinese medicine herbal formulations for immune dysfunction related illnesses. The effects of this medicinal mushroom on human colorectal cancer cells have not yet been evaluated. In this study, we investigated the effects of Ganoderma lucidum extract using SW 480 human colorectal cancer cell line. Materials and Methods: Two different fractions of Ganoderma lucidum extract, i.e., a fraction containing mainly polysaccharides (GLE-1), and a triterpenoid fraction without polysaccharides (GLE-2) were analyzed. Their antiproliferative activity was evaluated by cell proliferation assay and 3H-thymidine incorporation assay. Scavenging effects of DPPH radical were assessed using ESR-spectroscopy. Results: Our data showed that both GLE-1 and GLE-2 significantly inhibited the proliferation of SW 480 cells. The inhibitory effect of GLE-2 was much stronger than that of GLE-1. GLE-1 inhibited DNA synthesis in the cells and reduced the formation of DPPH radicals. Conclusion: Ganoderma lucidum extract inhibits proliferation of human colorectal cancer cells and possesses antioxidant properties.Цель: для лечения заболеваний, связанных с нарушениями функционирования иммунной системы, в традиционной китайской
медицине часто используют препараты на основе Ganoderma lucidum. В данной работе было изучено влияние экстракта Ganoderma
lucidum на клетки колоректального рака человека линии SW 480. Материалы и методы: изучали две фракции экстракта
Ganoderma lucidum: фракцию GLE-1, содержащую полисахариды, и тритерпеноидную фракцию GLE-2. Их рост-ингибирующую
активность определяли с помощью анализа клеточной пролиферации и по включению 3
H-тимидина. Для оценки антиоксидантной
активности использовали ЕСР-спектроскопию. Результаты: обе фракции Ganoderma lucidum подавляли пролиферацию клеток
SW 480. Рост-ингибирующий эффект GLE-2 был более выраженным, чем фракции GLE-1. Фракция GLE-1 подавляла синтез ДНК
в клетках линии SW 480 и понижала уровень формирования DPPH радикалов. Выводы: экстракт Ganoderma lucidum подавляет
пролиферацию клеток колоректального рака человека и обладает антиоксидантными свойствами
Density of states and magnetoconductance of disordered Au point contacts
We report the first low temperature magnetotransport measurements on
electrochemically fabricated atomic scale gold nanojunctions. As , the
junctions exhibit nonperturbatively large zero bias anomalies (ZBAs) in their
differential conductance. We consider several explanations and find that the
ZBAs are consistent with a reduced local density of states (LDOS) in the
disordered metal. We suggest that this is a result of Coulomb interactions in a
granular metal with moderate intergrain coupling. Magnetoconductance of atomic
scale junctions also differs significantly from that of less geometrically
constrained devices, and supports this explanation.Comment: 5 pages, 5 figures. Accepted to PRB as Brief Repor
A Self-Consistent First-Principles Technique Having Linear Scaling
An algorithm for first-principles electronic structure calculations having a
computational cost which scales linearly with the system size is presented. Our
method exploits the real-space localization of the density matrix, and in this
respect it is related to the technique of Li, Nunes and Vanderbilt. The density
matrix is expressed in terms of localized support functions, and a matrix of
variational parameters, L, having a finite spatial range. The total energy is
minimized with respect to both the support functions and the elements of the L
matrix. The method is variational, and becomes exact as the ranges of the
support functions and the L matrix are increased. We have tested the method on
crystalline silicon systems containing up to 216 atoms, and we discuss some of
these results.Comment: 12 pages, REVTeX, 2 figure
The Y(4260) as an omega chi_{c1} molecular state
It is suggested that the newly observed Y(4260) by BARBAR collaboration is a
molecular state composed of an omega and a chi_{c1}. Both the production and
decay properties are discussed. A consequence for this molecular state,
Y(4260), is that it decays into pi+pi-pi0 chi_{c1} with similar rate to pi+ pi-
J/psi. It is also expected that Y(4260) -> pi0 pi0 J/psi is produced at half
rate as Y(4260) ->pi+ pi- J/psi. These decay modes should be searched for in
the B factories using initial state radiative return data and B decay data as
well.Comment: 5 pages, 5 figure
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