2,295 research outputs found
Effect of alloying elements on magnesium alloy damping capacities at room temperature
Alloying is a good approach to increasing its strength but leads to a reduction of damping to pure magnesium. Classifying the alloying characteristics of various alloying elements in magnesium alloys and their combined effects on the damping and mechanical properties of magnesium alloys is important. In this paper, the properties of the Mg-0.6wt%X binary alloys were analyzed through strength measurements and dynamic mechanical analysis. The effects of foreign atoms on solid-solution strengthening and dislocation damping were studied comprehensively. The effect of solid solubility on damping capacity can be considered from two perspectives: the effect of single solid-solution atoms on the damping capacities of the alloy, and the effect of solubility on the damping capacities of the alloy. The results provide significant information that is useful in developing high-strength, high-damping magnesium alloys. This study will provide scientific guidance regarding the development of new types of damping magnesium alloys
Hadronic Charmed Meson Decays Involving Tensor Mesons
Charmed meson decays into a pseudoscalar meson P and a tensor meson T are
studied. The charm to tensor meson transition form factors are evaluated in the
Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the
Cabibbo-allowed decay is dominated by the
W-annihilation contribution and has the largest branching ratio in
decays. We argue that the Cabibbo-suppressed mode
should be suppressed by one order of magnitude relative to . When the finite width effect of the tensor resonances is taken
into account, the decay rate of is generally enhanced by a factor of
. Except for , the predicted branching ratios
of decays are in general too small by one to two orders of magnitude
compared to experiment. However, it is very unlikely that the
transition form factors can be enhanced by a factor of within the
ISGW quark model to account for the discrepancy between theory and experiment.
As many of the current data are still preliminary and lack sufficient statistic
significance, more accurate measurements are needed to pin down the issue.Comment: 11 page
Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices
We examine how the current--voltage characteristics of a doped weakly coupled
superlattice depends on temperature. The drift velocity of a discrete drift
model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated
as a function of temperature. Numerical simulations and theoretical arguments
show that increasing temperature favors the appearance of current
self-oscillations at the expense of static electric field domain formation. Our
findings agree with available experimental evidence.Comment: 7 pages, 5 figure
Design, Modeling, Microfabrication and Characterization of the Micro Gas Chromatography Columns
What on Earth have we been burning? Deciphering sedimentary records of pyrogenic carbon
Humans have interacted with fire for thousands of years, yet the utilization of fossil fuels marked the beginning of a new era. Ubiquitous in the environment, pyrogenic carbon (PyC) arises from incomplete combustion of biomass and fossil fuels, forming a continuum of condensed aromatic structures. Here we develop and evaluate 14C records for two complementary PyC molecular markers, benzene-polycarboxylic-acids (BPCAs) and polycyclic-aromatic-hydrocarbons (PAHs) preserved in aquatic sediments from a sub-urban and a remote catchment in the United States (U.S.) from mid-1700s to 1998. Results show that the majority of PyC stems from local sources and is transferred to aquatic sedimentary archives on sub-decadal to millennial time scales. Whereas a small portion stems from near-contemporaneous production and sedimentation, the majority of PyC (<90%) experiences delayed transmission due to ‘pre-aging’ on millennial timescales in catchment soils prior to its ultimate deposition. BPCAs (soot) and PAHs (precursors of soot) trace fossil fuel-derived PyC. Both markers parallel historical records of the consumption of fossil fuels in U.S., yet never account for more than 19% total PyC. This study demonstrates that isotopic characterization of multiple tracers is necessary to constrain histories and inventories of PyC, and that sequestration of PyC can markedly lag its production
Phenolic Compound Profiles in Grape Skins of Cabernet Sauvignon, Merlot, Syrah and Marselan Cultivated in the Shacheng Area (China)
The phenolic compounds in the grape skins of Cabernet Sauvignon (CS), Merlot (ML), Syrah (SY) and Marselan (MS) from Shacheng, in China, were compared using HPLC-MS/MS. The results showed that the types and levels of phenolic compounds varied greatly with cultivars. Malvidin derivatives were the main anthocyanins. CS and ML showed a higher content of malvidin-3-O-(6-O-acetyl)-glucoside than malvidin-3-O-(trans-6-O- coumaryl)-glucoside, while SY and MS differed from CS and ML. ML had higher delphinidin and cyanidin derivatives, SY had higher peonidin derivatives, while malvidin and petunidin were higher in MS. The total content of flavonols, flavan-3-ols, phenolic acids and stilbenes in grape skins showed no difference among CS, ML and MS. Isorhamnetin-3-O-glucoside (CS, ML, MY), quercetin-3O-glucoside (SY), procyanidin trimer (SY, MS), procyanidin dimer (CS, ML), syringetin-3-O-glucoside, trans-cinnamic acid and resveratrol were the most abundant non-anthocyanin phenolic compounds. Cluster analysis showed that CS and ML, and SY and MS had similar phenolic profiles
The Host Galaxies of X-ray Quasars Are Not Strong Star Formers
We use ultradeep SCUBA-2 850 μm observations (~0.37 mJy rms) of the 2 Ms Chandra Deep Field-North (CDF-N) and 4 Ms Chandra Deep Field-South X-ray fields to examine the amount of dusty star formation taking place in the host galaxies of high-redshift X-ray active galactic nuclei (AGNs). Supplementing with COSMOS, we measure the submillimeter fluxes of the 4–8 keV sources at , finding little flux at the highest X-ray luminosities but significant flux at intermediate luminosities. We determine graybody and MIR luminosities by fitting spectral energy distributions to each X-ray source and to each radio source in an ultradeep Karl G. Jansky Very Large Array (VLA) 1.4 GHz (11.5 μJy at ) image of the CDF-N. We confirm the far-infrared (FIR)-radio and mid-infrared (MIR)-radio correlations to z = 4 using the non-X-ray detected radio sources. Both correlations are also obeyed by the X-ray less luminous AGNs but not by the X-ray quasars. We interpret the low FIR luminosities relative to the MIR for the X-ray quasars as being due to a lack of star formation, while the MIR stays high due to the AGN contribution. We find that the FIR luminosity distributions are highly skewed and the means are dominated by a small number of high-luminosity galaxies. Thus, stacking or averaging analyses will overestimate the level of star formation taking place in the bulk of the X-ray sample. We conclude that most of the host galaxies of X-ray quasars are not strong star formers, perhaps because their star formation is suppressed by AGN feedback
Calculation of the γ-TiAl Lattice Resistance
The dislocation width and lattice resistance (Peierls stress) of a γ-TiAl alloy are calculated by the density ratio method. The lattice resistance is shown to decrease with the dislocation width. The relationship between the Peierls stress and dislocation width variation is defined by theoretical derivation. The yield stress is negatively correlated with the shear stress of the material. It can become a useful tool for choosing an appropriate shear stress under deformation.Методом отношения плотностей рассчитаны ширина дислокации и сопротивление решетки (напряжение Пайерлса). Результаты показывают, что сопротивление решетки уменьшается с увеличением ширины дислокации. Путем расчета получена зависимость между напряжением Пайерлса и дислокационным упрочнением, свидетельствующая о том, что предел текучести отрицательно коррелирует с напряжением сдвига материала. Поэтому она может дать полезную информацию для выбора соответствующего напряжения сдвига в процессе растяжения.Методом відносини щільностей розраховані ширина дислокації і опір решітки (напруження Пайерлса). Результати показують, що опір решітки зменшується зі збільшенням ширини дислокації. Шляхом розрахунку отримана залежність між напруженням Пайерлса і дислокаційним зміцненням, яка свідчить про те, що межа плинності негативно корелює з напруженням зсуву матеріалу. Тому вона може дати корисну інформацію для вибору відповідного напруження зсуву в процесі розтягування
Varied Signature Splitting Phenomena in Odd Proton Nuclei
Varied signature splitting phenomena in odd proton rare earth nuclei are
investigated. Signature splitting as functions of and in the angular
momentum projection theory is explicitly shown and compared with those of the
particle rotor model. The observed deviations from these rules are due to the
band mixings. The recently measured Ta high spin data are taken as a
typical example where fruitful information about signature effects can be
extracted. Six bands, two of which have not yet been observed, were calculated
and discussed in detail in this paper. The experimentally unknown band head
energies are given
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