Period Thickness Research Articles

Seasonal Variations on Quality Parameters of Pak Choi (Brassica rapa L. subsp. chinensis L.)

The aim of this study is to determine the changes in quality of pak choi in successive growing seasons. Experiments were carried out in a PE covered cold greenhouse in late autumn-early winter and late winter-early spring growing period in Turkey (41°11’ N, 27°49’ E). Results showed that morphological features, the leaf area (73.82 mm2), leaf length (31.21 mm), average leaf width (2.70 mm), maximum leaf width (3.92 mm), mass (95.27 g) and moisture content values of leaves (0.90% w.b.) were higher in late autumn-early winter period but leaf thickness (0.33 mm) contents were higher in late winter-early spring period. Yield characteristics investigated were affected by season and were found relatively higher in late autumn-early winter than late winter-early spring growing period. And it was 5713 kg ha-1 in late autumn-early winter growing period and 5034 kg ha-1 in late winter-early spring growing period. In point of the dry matter content investigated were affected by season, and were higher in late autumn-early winter than late winter-early spring growing period. It was 12.4% in late autumn-early winter growing period and 10.25% in late winter-early spring growing period. Account of total protein of plants grown in late autumn-early winter (25.16%) was higher than in late winter-early spring (22.45%) growing period. Sowing time did affect ascorbic acid content significantly. It was 44.21 mg.100-1 g in late autumn-early winter growing period and was recorded as 38.02 mg.100-1 g in late winter-early spring growing period. Color parametres L, a, b values were measured as 27.92; -6.98 and 8.53 in late autumn-early winter and as 21.64; -5.48; 7.49 late winter-early spring. Sowing time did affect color parameters content significantly. Late autumn-early winter growing time result was higher than in late winter-early spring growing time. With regard to mineral content N (4.67%), P (0.65%), Cu (9.32 ppm), Fe (879.6 ppm) and Zn (49.13 ppm) values were higher in plants grown in late autumn-early winter in comparison with plants grown in late winter-early spring as K (4.45%), Ca (2.36%), Mg (0.41%) and Mn (62.25 ppm) values of plants were higher in late winter-early spring growing period. Results of the study indicated that different weather conditions influenced the pak choi yield and the chemical composition of the leaf as well. Pak choi with its relatively short cultivating period, easy growing, and dietary value can be a good alternative crop for late autumn-early winter growing period in cold greenhouses.

Properties of Tunability and Stored Energy Density in the Ferroelectric Multilayers

Multilayers consisting of alternating ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer and relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) (P(VDF-TrFE-CFE)) terpolymer with different periodicities in thickness were prepared by the Langmuir-Blodgett method. Except for the dielectric and ferroelectric properties enhanced, the tunability also was enhanced in the multilayers with thinner periodic thickness. The polymer multilayers can be utilized for high energy density and low loss dielectrics, the multilayers with alternating 3 monolayers get the biggest high energy density. The reasons for the enhanced tunability and high energy density in the multilayer sample are discussed.

Sea ice floes dissipate the energy of steep ocean waves

Wave attenuation by ice floes is an important parameter for modelling the Arctic Oceans. At present, attenuation coefficients are extracted from linear models as a function of the incident wave period and floe thickness. Recent explorations in the Antarctic Mixed Ice Zone (MIZ) revealed a further dependence on wave amplitude, suggesting that nonlinear contributions are non-negligible. An experimental model for wave attenuation by a single ice floe in a wave flume is here presented. Observations are compared with linear predictions based on wave scattering. Results indicate that linear models perform well under the effect of gently sloping waves. For more energetic wave fields, however, transmitted wave height is normally over predicted. Deviations from linearity appear to be related to an enhancement of wave dissipation induced by unaccounted wave-ice interaction processes, including the floe over wash.

Exclusive Stereocomplex Crystallization of Linear and Multiarm Star-Shaped High-Molecular-Weight Stereo Diblock Poly(lactic acid)s.

Linear, 3-arm, and 6-arm star-shaped stereo diblock copolymers of l- and d-lactic acid (PLLA-b-PDLA) with high molecular weights (MWs) were synthesized via two-step ring-opening polymerization (ROP) with 1-dodechanol, glycerol, and d-sorbitol as the initiators, respectively. The chemical structure, nonisothermal and isothermal crystallization kinetics, crystalline structure, lamellar morphology, and mechanical thermal properties of PLLA-b-PDLAs with different macromolecular topologies were investigated. Compared to the high-molecular-weight (MW) poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic blends, PLLA-b-PDLAs exhibit faster crystallization upon cooling and isothermal melt crystallization; they crystallize exclusively in stereocomplex (sc) crystallites under all of the conditions investigated. This is attributable to the enhanced interactions between enantiomeric blocks linked covalently. Macromolecular topology influences the crystallization kinetics and crystalline structure of PLLA-b-PDLAs significantly. The crystallization temperature upon cooling, melting temperature, degree of crystallinity, spherulitic growth rate, crystallite size, long period, and crystalline layer thickness of PLLA-b-PDLA decrease with increasing branching number because of the retarding effect of branching on the crystallization rate and crystallizability. Because of the formation of high-melting-point sc crystallites, both the linear and star-shaped PLLA-b-PDLAs exhibit better thermal resistance and higher storage moduli at high temperature than does homocrystalline PLLA.

Structural characterization and low-temperature properties of Ru/C multilayer monochromators with different periodic thicknesses.

Ru/C multilayer monochromators with different periodic thicknesses were investigated using X-ray grazing-incidence reflectivity, diffuse scattering, Bragg imaging, morphology testing, etc. before and after cryogenic cooling. Quantitative analyses enabled the determination of the key multilayer structural parameters for samples with different periodic thicknesses, especially the influence from the ruthenium crystallization. The results also reveal that the basic structures and reflection performance keep stable after cryogenic cooling. The low-temperature treatment smoothed the surfaces and interfaces and changed the growth characteristic to a low-frequency surface figure. This study helps with the understanding of the structure evolution of multilayer monochromators during cryogenic cooling and presents sufficient experimental proof for using cryogenically cooled multilayer monochromators in a high-thermal-load undulator beamline.

Restoration of eroded stratal thickness in key periods of tectonic change in a multi-stage superimposed Tarim Basin in China

With an area of 56×104 km2, the Tarim Basin is the largest inland basin in China and is also generally acknowledged as one of the most important areas for potential oil and gas exploration. On the basis of data from 22 regional seismic profiles and 40 drilling wells, 15 important first-order and second-order regional unconformities were defined. Almost all the main unconformities are superimposed unconfomities. Since the Cambrian, 5 key periods of tectonic change have occurred during the evolution of the Tarim Basin. The total eroded stratal thickness of the above-mentioned unconformities was calculated by using the method of virtual extrapolation of seismic reflection. The results indicate that the total eroded stratal thickness of different periods is quite different in different locations of the basin. Taking the Upper-Middle Ordovician as an example, its thickness restoration of eroded strata was calculated into individual stages i.e. its thickness restoration of eroded strata was calculated to different tectonic periods. Otherwise, as for the specific period of tectonic change, the underlying strata were, respectively eroded and thus the thickness restoration of eroded strata was calculated into individual intervals. Taking the Early Hercynian period as an example, the eroded stratal thickness was calculated into individual intervals to calculate the ratio of intervals of various ages occupying the total eroded thickness. The results show that for the same stratum, its degree of erosion is quite different in different periods and at different locations, due to the varying influence of tectonic movement. The unconformities of some key periods of tectonic change have different controls on the degree of erosion and the eroded range of the individual period of the underlying strata which are the typical characteristics of multi-stage superimposition of unconformities in the Tarim Basin.

Dimensional Responses of Wood Under Cyclical Changing Temperature at Constant Relative Humidity

To investigate dimensional responses of wood under dynamic temperature condition, poplar (populous euramericana Cv.) specimens, 20 mm in radial (R) and tangential (T) directions with two thicknesses of 4 and 10 mm along the grain, were exposed to cyclic temperature changes in square wave between 25℃ and 40℃ at 60% relative humidity (RH) for three different cycling periods of 6 h, 12 h and 24 h. R and T dimensional changes measured during the cycling gave the following results: 1) Transverse dimensional changes of the specimens were generally square but at an opposite phase and lagged behind the imposed temperature changes. The phase lag was inversely correlated with cycling period, but positively related to specimen thickness, while the response amplitude was directly proportional to cycling period, but in a negative correlation with specimen thickness. 2) The specimens showed swelling hysteresis behavior. The heat shrinkage coefficient (HSC) became greater as cycling period increased or specimen thickness decreased. 3) Dimensional changes of the specimens produced deformation accumulation during repeated adsorption and desorption. The deformation accumulating ratio decreased with an increase in cycling period and specimen thickness. 4) Wood suffered 1.5 times as many dimensional changes per unit temperature variation as per unit humidity variation, and this deformation behaved even more seriously under static condition.

Tailoring crystallization behavior of poly (l-lactide) with a low molecular weight aliphatic amide

A low molecular weight aliphatic amide, N, N′-ethylenebis (12-hydroxystearamide) (EBH), was selected to tailor the crystallization behavior of poly (l-lactide) (PLLA). The effect of EBH on the crystallization kinetics, fine crystalline structure, and molecular mobility of PLLA has been systematically investigated. It has been found that the crystallizability of PLLA, including crystallization rate and crystallinity, can be promoted significantly by the addition of only 1 wt% EBH. Both the nucleation density and linear growth rate of spherulites have been improved, which together contributed to the decrease of overall crystallization time. The long period and lamellar thickness of PLLA crystals increased gradually with the isothermal crystallization temperature, whereas they were less influenced by the incorporation of EBH. Dynamic mechanical analysis proved that the mobility of PLLA chains was also increased in the presence of EBH. The accelerating effect of EBH on both the nucleation and molecular mobility of PLLA was supposed to be the hydrogen-bonding interaction between the hydroxyl groups in EBH and carboxyl groups in PLLA.

Stress engineering with AlN/GaN superlattices for epitaxial GaN on 200 mm silicon substrates using a single wafer rotating disk MOCVD reactor

Abstract

Engineering thermal transport in SiGe-based nanostructures for thermoelectric applications

Abstract

Study of Omnidirectional Reflection Bandgap Extension in One-Dimensional Quasi-Periodic Metallic Photonic Crystal

The reflection properties of light wave propagation in one-dimensional quasi-periodic metallic photonic crystal (PC) are comprehensively analyzed by transfer matrix method. In this work, we form a Fibonacci sequence quasi-periodic PC composed of metal and dielectric. The results demonstrate that the reflection stop band is strongly dependent on the periodic structure, metal thickness and incident angle. For this structure, the reflection stop band ranges from the visible light region to near-infrared region. Compared with the periodic metallic PC, the reflection stop bandwidth of our structure is wider. When the metal thickness increases, the reflection stop band is significantly enlarged. Furthermore, the reflection stop bandwidth slowly gets narrow and shifts to short wavelength region with the increase of incidence angle. Considering TE and TM wave at all incident angles, there is an omnidirectional reflection bandgap with width of 241nm for our investigated quasi-periodic metal PC.

A Comparison of Three Different Biodegradable Aliphatic Oligoesters (PGA, PLLA, and PCL) with Similar Linear Alkyl End Groups by DSC and SAXS

The biodegradable aliphatic oligoesters polyglycolide (PGA), poly(L-lactide) (PLLA), and poly(ϵ-caprolactone) (PCL) with similar number-average molecular weight Mn values but different linear alkyl end groups [CH3−[CH2−CH2]m−CH2−] were compared in terms of their physical properties, parameters such as melting temperature (Tm), crystallinity (xi), long period (L), and lamella thickness (D). They were analyzed by DSC and SAXS. The effect of a longer and nonpolar alkyl end group such as docosyl [CH3−[CH2−CH2]10−CH2−] on the long period (L) was more evident for PCL because it was the most nonpolar species in the family of oligoesters analyzed.

Relating wave attenuation to pancake ice thickness, using field measurements and model results

AbstractWave attenuation coefficients (α, m−1) were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the Weddell Sea. Data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low‐pressure system. Attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken‐floe marginal ice zones. A clear linear relation between α and ice thickness was demonstrated, using ice thickness from a novel dynamic/thermodynamic model. A simple expression for α in terms of wave period and ice thickness was derived, for application in research and operational models. The variation of α was further investigated with a two‐layer viscous model, and a linear relation was found between eddy viscosity in the sub‐ice boundary layer and ice thickness.

High reflectance Cr/C multilayer at 250 eV for soft X-ray polarimetry

X-ray reflection near 45° via multilayer mirrors can be used for astronomical polarization measurements. A Cr/C multilayer mirror (designed for X-ray polarimetry at 250eV), with a period thickness of 3.86nm and a bi-layer number of 100, was fabricated using direct current magnetron sputtering. Grazing incidence X-ray reflectometry at 8keV and transmission electron microscopy were used to investigate the multilayer structure. Different models were introduced to fit the hard X-ray reflectivity curve, which indicates that the layer thickness of two materials slightly drifts from the bottom to the top of the stack. Both the chromium and carbon layers are amorphous with asymmetric interfaces, while the Cr-on-C interface is slightly wider. Based on the good quality of the multilayer structure, a high reflectivity of 21.8% for the s-polarized light was obtained at 250eV at a grazing incidence angle of 40.7°. The fabricated Cr/C multilayer mirror exhibits high reflectivity and polarization levels in the energy region of 240eV–260eV.

Thermally induced interface changes in W/B4C multilayers

Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer thickness to period thickness) as a function of annealing temperatures were studied by grazing incidence X-ray reflectivity (GIXRR), and grazing incidence X-ray diffraction (GIXRD). Both period thickness expansion and compression were observed depending upon Γ and annealing temperatures. Multilayer with the W layer thickness close to the B4C layer has undergone less period thickness changes. Successive appearance and disappearance of multilayer Bragg maxima in GIXRR were observed. Such behavior suggested that redistribution of atomic density within bilayer, the displacement of interface and the multilayer period thickness change as annealing proceeds. GIXRD measurements performed using synchrotron radiation suggested the formation of phases corresponding to tungsten boride and carbide.

Lithium Transport through Thin Silicon Layers: On the Origin of Bragg Peaks in Neutron Reflectometry Experiments

Lithium transport through ultrathin silicon layers can be measured non-destructively by neutron reflectometry (NR) using a multilayer composed of silicon layers embedded between solid state Li reservoirs. An established model system is a multilayer with a repetition of five [Si / natLiNbO3 / Si / 6LiNbO3] units. Two types of Bragg peaks are detectable in reflectivity patterns. These Bragg peaks result from the interference of neutrons reflected at periodic interfaces. One type of Bragg peak originates from the periodicity of the LiNbO3/Si chemical contrast (first order peak), while the other Bragg peak results from a superstructure with double periodicity. This superstructure may arise from 6Li/7Li isotope contrast or alternatively from periodic thickness variations, as shown by simulations based on the Parratt algorithm. The intention of the present paper was to elucidate the origin of the second Bragg peak. Experiments done by Secondary Ion Mass Spectrometry (SIMS) isotope sensitive depth profiling showed in a direct way that annealing at 360 °C destroys indeed the 6Li/7Li contrast, whereas the LiNbO3/Si chemical contrast remains unchanged. This evidences that the experimentally observed decrease of the second Bragg peak in the reflectivity pattern during annealing is a measure for Li transport through the Si layer.

GaNAs/InGaAs Superlattice Solar Cells with High N Content in the Barrier Grown by All Solid-State Molecular Beam Epitaxy**Supported by the National Natural Science Foundation of China under Grant No 61274134, the University of Science and Technology Beijing Talents Start-up Program under Grant No 06105033, and the International Cooperation Projects of Suzhou City under Grant No SH201215.

We demonstrate nearly 1 eV GaN0.03As0.97/In0.09Ga0.91As strain-compensated short-period superlattice solar cells by all solid-state molecular beam epitaxy. The optimal period thickness for the superlattice growth is achieved to realize high structural quality. Meanwhile, the annealing conditions are optimized to realize a photoluminescence (PL) at a low temperature. However, no PL signal is detected at room temperature, which could be reflected by a lower open-circuit voltage of the fabricated devices. The GaN0.03As0.97/In0.09Ga0.91As superlattice solar cells show a reasonably-high short-circuit current density (Jsc) of over 10 mA/cm2. Furthermore, a concentration behavior is measured, which shows a linear relationship between Jsc and concentration ratios. The extrapolated ideality factor and saturated current density by the concentration action are in good agreement with that extracted by the dark case of the p-i-n diodes.

Surface Plasmon Polaritons on Silver Gratings for Optimal SERS Response

One of the most important obstacles for the application of surface enhanced Raman spectroscopy (SERS) is the poor reproducibility of SERS active substrates: SERS intensity can be varied from one substrate to another and moreover along the one substrate surface. Reproducible SERS substrate can be prepared through introduction of highly ordered metal array, where light focusing is achieved through excitation of surface plasmon-polaritons (SPPs). In this work, excimer laser patterning of poly(methyl methacrylate) followed by silver evaporation is proposed as an effective way for the creation of reproducible and effective surface plasmon-polaritons (SPP)-based SERS substrate. Detailed theoretical and experimental studies were performed to optimize structure parameter for effective SPP excitation. It was found that the narrow range of grating periodicity and metal thickness exist, where SPPs can be most efficiently excited. Despite the fact that SERS response was almost always achieved, the enhancement factor ...

Thermal flux limited electron Kapitza conductance in copper-niobium multilayers

We study the interplay between the contributions of electron thermal flux and interface scattering to the Kapitza conductance across metal-metal interfaces through measurements of thermal conductivity of copper-niobium multilayers. Thermal conductivities of copper-niobium multilayer films of period thicknesses ranging from 5.4 to 96.2 nm and sample thicknesses ranging from 962 to 2677 nm are measured by time-domain thermoreflectance over a range of temperatures from 78 to 500 K. The Kapitza conductances between the Cu and Nb interfaces in multilayer films are determined from the thermal conductivities using a series resistor model and are in good agreement with the electron diffuse mismatch model. Our results for the thermal boundary conductance between Cu and Nb are compared to literature values for the thermal boundary conductance across Al-Cu and Pd-Ir interfaces, and demonstrate that the interface conductance in metallic systems is dictated by the temperature derivative of the electron energy flux in the metallic layers, rather than electron mean free path or scattering processes at the interface.

Theoretical study of the effects of strain balancing on the bandgap of dilute nitride InGaSbN/InAs superlattices on GaSb substrates

The addition of nitrogen to III–V alloys has been widely studied as a method of modifying the band gap for mid-infrared (IR) applications. Lattice matching these alloys to convenient substrates such as GaSb, however, is challenging due to the significantly different lattice constants. One approach is to use InGaSbN/InAs grown on GaSb where the InGaSbN layer has a larger lattice constant than the substrate, and the InAs layer has a lower lattice constant, and thus the compressive and tensile stress of the superlattice layers can be balanced in a so called strained-layer superlattice. In this paper, we report InxGa1−xSb1−yNy/InAs strained-layer superlattices with type-II (staggered) energy offsets on GaSb substrates, where the design of the layer thickness is based on the lattice constants and the elastic moduli. Three different strain balance conditions are reported: fixed superlattice period thickness, fixed InAs well thickness, and fixed InxGa1−xSb1−yNy barrier thickness. Eight-band k·p simulations of these structures were used to analyze the superlattice miniband energies. For fully strain balanced InxGa1−xSb1−yNy/InAs superlattices lattice matched to the GaSb substrate, careful consideration of strain balance conditions was needed to achieve a lower effective miniband gap needed for longer cutoff wavelength detectors. For non-strained balanced InxGa1−xSb1−yNy/InAs superlattices, long-wavelength cutoff up to 8μm can be achieved as part of a trade-off between the deleterious effects of strain and the reduction of the barrier band gap through N incorporation.