Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 29
Filtrar
Mais filtros










Base de dados
Tipo de estudo
Intervalo de ano de publicação
1.
J Child Lang ; 46(4): 707-732, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-30935433

RESUMO

Parameter setting is either precipitous (Gibson & Wexler, 1994) or it is gradual in response to input frequency (Yang, 2002, 2004). In this study, we compare these models against the empirical domain of subject and (direct) object drop in Mandarin. We conducted a corpus-based study of the speech of 47 Mandarin-speaking children aged 1;2-6;5, and their caregivers, from the CHILDES database. The results show that before age 1;8 all the children used null subjects and null objects in a target-like fashion, which reveals that the parameter that governs null topics is set from very early on, even if the presence of disambiguating evidence for [+Null Topic] patterns is low. Besides, children's ba constructions, which require an overt object, reliably included this object from the first occurrence although its frequency was scarce in the input. Our results indicate that the setting of certain parameters occurred early independently of the input.

2.
J Nanosci Nanotechnol ; 19(1): 593-601, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30327074

RESUMO

The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

3.
J Nanosci Nanotechnol ; 19(1): 609-612, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30327076

RESUMO

The working wavelength of Ni-like, Ta soft X-ray laser is 44.8 Å, just near the "water window." High reflection multilayers are required for this kind of laser in China. In this work, we design and fabricate carbon-based multilayer reflective samples. The Cr/C multilayer was selected from proposed candidates such as Co/C, Ni/C, and CoCr/C material combinations. The period thickness is only 22.6 Å. Cr/C multilayers were deposited by the magnetron sputtering method. Multilayers with bi-layer numbers of 150, 200, 250 and 300 were deposited onto super polished silicon wafers. All multilayers have been characterized by grazing incidence X-ray reflectance (GIXRR). Then, near-normal incidence reflectance measurements were performed at beamline 3W1B, Beijing synchrotron radiation (BSRF). The highest reflectance of 13.2% is achieved with the bi-layer number of 300. Transmission electron microscopy measurements also clearly show the sharp Cr-C interfaces in the multilayer.

4.
Opt Express ; 26(18): 23132-23141, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-30184968

RESUMO

The total internal reflection restricts light extraction efficiency of scintillator, leading to reduced detection efficiency and signal-to-noise ratio in the field of scintillator-based radiation detection system. This research presents the method of applying microlens arrays to improve the light extraction efficiency as well as achieve directional control of emission for scintillators. For BGO (Bi4Ge3O12) scintillator covered with PMMA (polymethyl-methacrylate) hemispherical microlens array, the 2.59-fold in particular angle (θem = 45°) and overall 1.94-fold angle-integrated enhancement ratios have been obtained. Furthermore, we analyze and optimize some parameters of microlens arrays such as the packing arrangement, duty ratio, size, refractive index, and shape. As a result, when the refractive index of microlens is slightly larger than that of scintillator, a maximum 6.23-fold angle-integrated enhancements can be achieved. It can be concluded that the microlens array covered on scintillator has considerable value for practical applications on radiation detection.

5.
J Synchrotron Radiat ; 25(Pt 3): 785-792, 2018 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-29714189

RESUMO

The interior structure, morphology and ligand surrounding of a sputtering-deposited chromium monolayer and Cr/C and Cr/Sc multilayers are determined by various hard X-ray techniques in order to reveal the growth characteristics of Cr-based thin films. A Cr monolayer presents a three-stage growth mode with sudden changes occurring at a layer thickness of ∼2 nm and beyond 6 nm. Cr-based multilayers are proven to have denser structures due to interfacial diffusion and layer growth mode. Cr/C and Cr/Sc multilayers have different interfacial widths resulting from asymmetry, degree of crystallinity and thermal stability. Cr/Sc multilayers present similar ligand surroundings to Cr foil, whereas Cr/C multilayers are similar to Cr monolayers. The aim of this study is to help understand the structural evolution regulation versus layer thickness and to improve the deposition technology of Cr-based thin films, in particular for obtaining stable Cr-based multilayers with ultra-short periods.

6.
Opt Express ; 26(9): 11438-11446, 2018 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-29716062

RESUMO

Plastic scintillators are widely used in various radiation measurement systems. However, detection efficiency and signal-to-noise are limited due to the total internal reflection, especially for weak signal detection situations. In the present investigation, large-area photonic crystals consisting of an array of periodic truncated cone holes were prepared based on hot embossing technology aiming at coupling with the surface of plastic scintillator to improve the light extraction efficiency and directionality control. The experimental results show that a maximum enhancement of 64% at 25° emergence angle along Γ-M orientation and a maximum enhancement of 58% at 20° emergence angle along Γ-K orientation were obtained. The proposed fabrication method of photonic crystal scintillator can avoid complicated pattern transfer processes used in most traditional methods, leading to a simple, economical method for large-area preparation. The photonic crystal scintillator demonstrated in this work is of great value for practical applications of nuclear radiation detection.

7.
J Synchrotron Radiat ; 25(Pt 2): 378-384, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29488916

RESUMO

Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length λu = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes-Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 µm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes-Poincaré parameters for all linear angles would require alteration of both these aspects.

8.
Nanoscale ; 10(7): 3148-3152, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29384167

RESUMO

To meet the increasing requirements of minimizing circuits, the development of novel device architectures that use ultra-thin two-dimensional materials is encouraged. Here, we demonstrate a non-volatile black phosphorus (BP) PNP junction in a BP/h-BN/graphene heterostructure in which BP acts as a transport channel layer, hexagonal boron nitride (h-BN) serves as a tunnel barrier layer and graphene is the charge-trapping layer. The device architecture is designed such that only the middle part of the BP is aligned over the graphene flake, enabling the flexible tuning of the charge carriers in the BP over the graphene charge-trapping layer. Thus, the device exhibits the ability to work in two different operating modes (PNP and PP+P). Each operating mode can be retained well and demonstrates non-volatile behavior, and each can be programmed by using the control-gate.

9.
Dent Mater J ; 35(4): 659-67, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27477233

RESUMO

This study investigates the anti-bacterial property of Ti-Cu sintered alloys against Porphyromonas gingivalis. The anti-anaerobic property of Ti-Cu sintered alloys against P. gingivalis was investigated by antibacterial activity test, DNA measurement, DAPI staining and morphology observation. The antibacterial rates of the Ti-5Cu against P. gingivalis after 18 and 24 h incubation were 36.04 and 54.39%, and those of Ti-10Cu were 68.69 and 75.39%, which were lower than their anti-aerobic abilities. The concentration of P. gingivalis DNA gradually decreased with the increasing Cu content, which was nearly 50% after 24 h incubation on Ti-10Cu. SEM results showed that the shape of P. gingivalis changed and the bacteria broke apart with the addition of Cu and the extension of the culture time. Ti-Cu sintered alloys could not only kill anaerobic bacteria but also reduce the activity of the survived bacteria. The anti-anaerobic mechanism was thought to be in associated with the Cu ion released from Ti-Cu alloy.


Assuntos
Cobre , Ligas Dentárias , Porphyromonas gingivalis , Titânio , Antibacterianos , Teste de Materiais
10.
J Synchrotron Radiat ; 22(6): 1419-25, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26524307

RESUMO

The characterization of Mg-Co-Zr tri-layer stacks using X-ray fluorescence induced by X-ray standing waves, in both the grazing-incidence (GI) and the grazing-exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr] × 30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] × 30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. An explanation of this opposite behavior of the Co-on-Zr and Zr-on-Co interfaces is given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/CoxZry bi-layer stack, with x/y estimated around 3.5.

11.
J Synchrotron Radiat ; 21(Pt 1): 97-103, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24365922

RESUMO

An integration method is demonstrated for directly determining the average interface statistics of periodic multilayers from the X-ray scattering diagram. By measuring the X-ray scattering diagram in the out-of-plane geometry and integrating the scattered intensity along the vertical momentum transfer qz in an interval, which is decided by the thickness ratio Γ (ratio of sublayer's thickness to periodic thickness), the cross-correlations between different interfaces are canceled and only the autocorrelations are reserved. Then the multilayer can be treated as a `single interface' and the average power spectral density can be obtained without assuming any vertical correlation model. This method has been employed to study the interface morphology of sputter-deposited W/Si multilayers grown at an Ar pressure of 1-7 mTorr. The results show an increase in vertical correlation length and a decrease in lateral correlation length with increased Ar pressure. The static roughness exponent α = 0 and dynamic growth exponent z = 2 indicate the Edwards-Wilkinson growth model at an Ar pressure of 1-5 mTorr. At an Ar pressure of 7 mTorr, α = 0.35 and z = 1.65 indicate the Kardar-Parisi-Zhang growth model.

12.
Rev Sci Instrum ; 84(7): 073705, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23902074

RESUMO

A novel EUV four channels normal incidence imaging system for plasma diagnostics of Z-pinch facility was presented in this paper, which consists of four concave mirrors and one convex mirror used for focusing an object onto four different positions with about 30 µm resolution on the same image plane. In addition, this imaging system can work at the energies of 50 eV, 95 eV, 150 eV, and broadband of 50-100 eV by using different multilayer films deposited on the concave and convex mirrors. This instrument, combined with framing camera, can achieve the power of two-dimensional spatial and temporal resolution, as well as the ability to imaging the plasma at the specific temperature. In the paper, the four channels microscope centering at multi-energies was developed.

13.
J Synchrotron Radiat ; 20(Pt 3): 449-54, 2013 May.
Artigo em Inglês | MEDLINE | ID: mdl-23592624

RESUMO

B4C-based multilayers have important applications for soft to hard X-rays. In this paper, X-ray grazing-incidence reflectivity and diffuse scattering, combining various analysis methods, were used to characterize the structure of B4C-based multilayers including layer thickness, density, interfacial roughness, interdiffusion, correlation length, etc. Quantitative results for W/B4C, Mo/B4C and La/B4C multilayers were compared. W/B4C multilayers show the sharpest interfaces and most stable structures. The roughness replications of La/B4C and Mo/B4C multilayers are not strong, and oxidations and structure expansions are found in the aging process. This work provides guidance for future fabrication and characterization of B4C-based multilayers.


Assuntos
Compostos de Boro/química , Carbono/química , Lentes , Refratometria/instrumentação , Raios X , Compostos de Boro/efeitos da radiação , Carbono/efeitos da radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Teste de Materiais , Espalhamento de Radiação
14.
ACS Appl Mater Interfaces ; 5(2): 404-9, 2013 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-23245346

RESUMO

X-ray standing waves generated by periodic multilayers have been used to characterize the interface microstructures of Ti/Ni/Ti trilayers based on the X-ray reflectivity (XRR) and grazing incidence X-ray fluorescence (GIXRF) methods. For the Ni layer having thickness of 1.7 nm, it is observed that the roughness of Ti-on-Ni interface is 0.64 nm and that of Ni-on-Ti interface is 0.40 nm, which can be explained by an additional roughness on the Ti-on-Ni interface induced by the nucleation of Ni crystallites when the Ni layer thickness is at the amorphous-to-crystalline transition region. For the Ni layer thickness of 3.3 nm beyond this transition region, the roughness of Ti-on-Ni interface is 0.42 nm and Ni-on-Ti interface is 0.46 nm, which is consistent with the expectation on wetting and dewetting conditions.

15.
J Synchrotron Radiat ; 19(Pt 6): 944-8, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23093753

RESUMO

Two APPLE II undulators installed on the Diamond I10 beamline have all four magnet arrays shiftable and thus can generate linear polarization at any arbitrary angle from 0° to 180°, as well as all other states of elliptical polarization. To characterize the emitted radiation polarization state from one APPLE II undulator, the complete polarization measurement was performed using a multilayer-based soft X-ray polarimeter. The measurement results appear to show that the linear polarization angle offset is about 6° compared with other measurements at 712 eV, equivalent to an undulator jaw phase offset of 1.1 mm. In addition, the polarization states of various ellipticities have also been measured as a function of the undulator row phase.

16.
Rev Sci Instrum ; 83(5): 053114, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22667609

RESUMO

The geometrical factor in the grazing incident x-ray fluorescence analysis is an important angle-dependent term, which can have a great effect on the measured data. In this paper, the effects of the geometrical factor on the florescence yield have been demonstrated. A formula is presented to estimate the geometrical factor, which includes the experimental parameters of the beam and setup. The validity of this formula is proven by the good agreement between the calculated fluorescence yields with the experimental results in grazing incident x-ray fluorescence analysis.

17.
Opt Express ; 20(10): 10692-700, 2012 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-22565694

RESUMO

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers for extreme ultraviolet (EUV) optics were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. The comparison of the two systems shows that the Al(1%wtSi)/Zr multilayers have the lowest interfacial roughness and highest reflectivity. Based on the X-ray diffraction, the performance of the two systems is determined by the crystallization of Al layer. To fully understand the Al(1%wtSi)/Zr multilayer, we built up a two-layer model to fit situation of the AFM images, and simulate the grazing incident x-ray reflection-measurements of multilayers with various periods (N = 10, 40, 60, 80). Below 40 periods, the roughness components are lowered. After 40 periods, both surface and interfacial roughness increase with the period number, and decrease the reflectance. According to transmission electron microscope images, the model can represent the variable structure of the system.


Assuntos
Alumínio/química , Óptica e Fotônica , Zircônio/química , Cristalização/métodos , Desenho de Equipamento , Magnetismo , Teste de Materiais , Microscopia de Força Atômica/métodos , Microscopia Eletrônica de Transmissão/métodos , Propriedades de Superfície , Difração de Raios X , Raios X
18.
Opt Lett ; 37(3): 299-301, 2012 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-22297332

RESUMO

We studied infrared normal spectral emissivity on quasi-periodic microstructured silicon, which was prepared by femtosecond laser irradiation in SF6 ambient gas, coated with 100 nm thick Au thin film. The observed emissivity is higher than any reported previously for a flat material with a thickness of less than 0.5 mm, at a temperature range of 200 °C to 400 °C. The emissivity over the measured wavelength region increases with temperature and the spike height. These results show the potential to be used as a flat blackbody source or for applications in infrared thermal sensor, detector, and stealth military technology.

19.
Opt Express ; 19(22): 21849-54, 2011 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-22109036

RESUMO

The efficiency of B(4)C, Mo and Zr barrier layers to improve thermal stability of Mg/Co multilayer up to 400 °C is investigated. Multilayers were deposited by direct current magnetron sputtering and characterized using X-ray and extreme ultraviolet reflection. The results suggest that B(4)C barrier layer is not effective due to drastic diffusion at Mg-B(4)C interface. Although introducing Mo barriers improves the thermal stability from 200 to 300 °C, it increases the interface roughness and thus degrades the optical performances. On the contrary, Zr barriers can significantly increase the thermal stability of Mg/Co up to 400 °C without optical performance degradation. Thus, Mg/Zr/Co/Zr is suitable for EUV applications requiring both optimal optical performances and heat resistance.

20.
Opt Express ; 19(17): 15929-36, 2011 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-21934956

RESUMO

The direct replication of W/Si multilayers and the effect of separating layer thickness on the performance of the multilayer before and after replication are investigated systematically. Platinum separating layers with different layer thicknesses were first deposited onto different supersmooth mandrels and then W/Si multilayers with the similar structure were deposited onto these Pt-coated mandrels by using a high vacuum DC magnetron sputtering system. After the deposition, these multilayers were replicated onto the commercially available float glass substrates by epoxy replication technique. These multilayers before and after replication are characterized by grazing-incident X-ray reflectance measurement and atomic force microscope. The measured results show that before and after replication, the reflectivity curves are much similar to those calculated and the surface roughness of each sample is close to that of the mandrel, when the separating layer thickness is larger than 1.5 nm. These results reveal that the W/Si multilayer with the separating layer thickness larger than 1.5 nm can be successfully replicated onto a substrate without modification of the structure, significant increase of surface roughness or apparent change of reflectivity.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA