| 18231. |
- Zhang, Jianming, et al.
(författare)
-
Novel evaluation method of neutron reflectivity data applied to stimulus-responsive polymer brushes
- 2008
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 4:3, s. 500-509
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectivity (NR) measurements have been performed on stimulus-responsive polymer brushes containing N-isopropylacrylamide (NIPAAM) at different temperatures and contrasts using two different brush samples of roughly the same grafting density and layer thickness. The NR data were analyzed using a novel method employing polymer density profiles predicted from lattice mean-field theory augmented with a polymer model to describe polymer solubility that decreases with increasing temperature. The predicted density profiles at the different temperatures were self-consistent with the experimentally observed profiles; hence the experimental data lend credibility to the theory. We found that the brush thickness decreased from 220 to 160 nm and the polymer volume fraction increased from 55 to 75% when increasing temperature from 293 to 328 K. The new evaluation approach involved significantly fewer independent fitting parameters than methods involving layers of uniform densities. Furthermore, the approach can straightforwardly be extended to analyze neutron reflectivity data of grafted, weakly charged polymers that display pH-sensitive behaviour and also to block copolymers and to surfaces with adsorbed polymers. We propose that such accurate model calculations provide a tool to interpret results from NR experiments more effectively and design neutron reflectivity experiments for optimal outcome.
|
|
| 18232. |
- Zhang, Jinyun, et al.
(författare)
-
UWB Systems for Wireless Sensor Networks
- 2009
-
Ingår i: Proceedings of the IEEE. - 0018-9219. ; 97:2, s. 313-331
-
Tidskriftsartikel (refereegranskat)abstract
- Wireless sensor networks are emerging as an important area for communications. They enable a wealth of new applications including surveillance, building control, factory automation, and in-vehicle sensing. The sensor nodes have to operate under severe constraints on energy consumption and form factor, and provide the ability for precise self-location of the nodes. These requirements can be fulfilled very well by various forms of ultra-wide-band (UWB) transmission technology. We discuss various techniques and tradeoffs in UWB systems and indicate that time-hopping and frequency-hopping impulse radio physical layers combined with simple multiple-access techniques like ALOHA are suitable designs. We also describe the IEEE 802.15.4a standard, an important system that adopts UWB impulse radio to ensure robust data communications and precision ranging. in order to accommodate heterogeneous networks, it uses specific modulation, coding, and ranging waveforms that can be detected well by both coherent and noncoherent receivers.
|
|
| 18233. |
- Zhang, Jin-Yan, et al.
(författare)
-
Dimethylsulfoxide-soluble Smoking Particles and Nicotine Affect Vascular Contractibility
- 2009
-
Ingår i: Archives of Pharmacal Research. - : Springer Science and Business Media LLC. - 1976-3786 .- 0253-6269. ; 32:10, s. 1475-1481
-
Tidskriftsartikel (refereegranskat)abstract
- The aim is to study the effect of dimethylsulfoxide-soluble smoking particles (DSP) and nicotine on the contractility of rat mesenteric artery. The superior mesenteric artery segments were cultured with DSP or nicotine for 24 h. The vascular contractibility was recorded with myograph system. DSP 0.4 mL/L and nicotine 0.48 and 0.96 mg/L shifted the concentration-contractile curves induced by sarafotoxin 6c, a selective agonist for ETB receptor toward the left with increased E-max. DSP 0.4 mL/L and nicotine 0.96 mg/L shifted ETA receptor-mediated the concentration-contractile curves toward the left with increased E-max. However, nicotine 0.06 mg/L which is the equivalent concentration of nicotine in DSP 0.4 mL/L did not affect the curves and the E-max mediated with ETA receptor and ETB receptor. DSP 0.2 and 0.4 mL/L shifted the concentration-contractile curves induced by noradrenaline toward the right with decreased E-max. Neither did nicotine 0.06 and 0.96 mg/L. Both DSP and nicotine shifted the concentration-contractile curves induced by 5-hydroxytryptamine (5-HT) toward the right parallely. DSP changed the phenotypes towards an increased efficacy of ETA receptor and ETB receptor, and a reduced efficacy of 5-HT receptor and alpha-adrenocceptor. The effects of DSP on ETB receptor, ETA receptor and alpha-adrenocceptor were independent of nicotine. The effect on 5-HT receptor was responsible to nicotine.
|
|
| 18234. |
- Zhang, Lebo, et al.
(författare)
-
Coherent electron flow from a double slit with slit widths in the quantum conductance regime
- 2006
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 18:49, s. 11103-11119
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a theoretical study of the quantum interference behaviour of electron flow from a double-slit device made from a semiconductor two-dimensional electron gas (2DEG) system with the slit widths in the quantum conductance regime. The device consists of a double slit and a single slit in a configuration where the single slit is placed on the source side of the double slit. The wavefunctions of electrons passing through the double-slit structure are calculated on the basis of a scattering matrix method. It is found that including a single slit between the double slit and the source contact in the device is essential for the observation of interference fringes of electron flow in a double-slit experiment with a 2DEG. When only the lowest mode is open for conduction in the individual slits, the interference patterns of electron flow from the double slit resemble the results of a conventional Young's double-slit experiment well. When several modes are open for conduction in the individual slits, the interference patterns of electron flow from the double slit are dominated by the interference of electrons flowing through the highest index open modes in the slits. As a result of the existence of multiple-lobe structures in electron flow from these high index open modes, these interference patterns, in general, show rather complex structures. We also discuss the characteristics of interference patterns in the near-and far-field regimes and the dependence of the fringe spacing on the slit distance in the double slit.
|
|
| 18235. |
|
|
| 18236. |
- Zhang, Lebo, et al.
(författare)
-
Multimode electron transport through quantum waveguides with spin-orbit interaction modulation: Applications of the scattering matrix formalism
- 2005
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:4
-
Tidskriftsartikel (refereegranskat)abstract
- We present a formulation of the scattering matrix method for spin-dependent electron transport in a quantum waveguide with spin-orbit interaction (SOI). All the required Hamiltonian matrices needed in the implementation of the formulation are represented in a basis of the transverse spatial eigenstates and the spin eigenstates of the leads. Thus the method has great flexibility and can be easily applied to systems with complex geometrical structure, potential distribution, and SOI strength profile. Also, the method is numerically stable and can be used to treat spin-dependent multisubband scattering processes accurately. We have applied the method to the spin-dependent electron transport in quasi-one-dimensional (Q1D) conductors, with a region of the Rashba SOI of uniform strength and with a region containing a Rashba SOI superlattice, made from a semiconductor heterostructure. The total conductance, spin-dependent conductances, and spin polarization of the system are calculated for a fully spin-polarized electron beam injected from a lead into the SOI region. For the Q1D conductor with a single region of the Rashba SOI, it is found that when the Fermi energy is set at a value, for which the total conductance is at a plateau, the spin-dependent conductances show regular oscillations with increasing SOI strength. This is approximately true even when the total conductance is at a high plateau and thus multiple subbands in the waveguide are open for conduction. However, when the Fermi energy is set at a value close to the onset of a subband (with the subband index n >= 2), the spin-polarized conductances plotted against the SOI strength and the SOI region length show sharp resonance features or complex fluctuations. These irregular conductance characteristics arise from SOI-induced strong coupling between subbands. For the Q1D conductor modulated by an array of strong Rashba SOI stripes, the total conductance shows regular superlattice behavior, while the spin-dependent conductances show complex behavior with regions of slow oscillations and regions of rapid oscillations. As in the Q1D conductor with a single SOI region, the slow oscillations are found in the energy regions where the total conductance is at plateaus. However, the rapid oscillations appear at energies close to the onsets of subbands with the subband index n >= 2. These oscillations originate from strong spin scattering by localized states formed in the SOI-modulated superlattice region.
|
|
| 18237. |
- Zhang, Lebo, et al.
(författare)
-
Scattering matrix method for multimode electron transport through quantum wires under a local magnetic field modulation and spin-orbit interaction
- 2006
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 74:19
-
Tidskriftsartikel (refereegranskat)abstract
- A generalized scattering matrix method is presented for spin-dependent electron transport in a quantum waveguide under the modulations of local magnetic field and/or spin-orbit interaction (SOI). All the required Hamiltonian matrices are expressed in terms of a common basis spanned by the products of the transverse spatial eigenstates and the spin eigenstates of the leads. In the formulation we have included an additional SOI term caused by an in-plane electric potential modulation and have assumed a free choice of magnetic vector potential. Thus the method can easily be applied to two-dimensional electron gas systems with complex geometrical structure, SOI strength profile, distributions of electric potential and magnetic field, etc. The method is numerically stable and can be used to treat accurately spin-dependent, multisubband, electron scattering processes. As an application, the method has been implemented for a Rashba SOI wire subject to a local magnetic field generated by a single ferromagnetic metal stripe on top. In the absence of the magnetic field, the conductance of electrons passing through the SOI region shows a series of Fano-resonance type dips in the vicinity of the onsets of subbands (with the subband index n >= 2). When the local magnetic field is present, the degeneracy of SOI-induced bound states is removed, leading to splittings of these conductance dips. At two split conductance dips originated from the same degenerate dip, a remarkable difference is found in the spatial distribution of spin-projected probability and in the spatial distribution of local spin polarization. It is seen that for a Rashba wire a Hall-like spin accumulation appears at the conductance dips at zero magnetic field. However, in the presence of a local magnetic field a separation of opposite spins along the transport direction is observed in the Rashba wire. In contrast, the zitterbewegung oscillations can show up, when the conductance is at a plateau, and disappear, when the conductance is at a Fano-resonance type dip, regardless the presence of the local magnetic field.
|
|
| 18238. |
- Zhang, Mengliang, et al.
(författare)
-
Expression of calcium channel Ca(v)1.3 in cat spinal cord: Light and electron microscopic immunohistochemical study
- 2008
-
Ingår i: Journal of Comparative Neurology. - : Wiley. - 1096-9861 .- 0021-9967. ; 507:1, s. 1109-1127
-
Tidskriftsartikel (refereegranskat)abstract
- In spinal neurons, plateau potentials serve to amplify neuronal input signals. To a large extent, the underlying persistent inward current is mediated by a subtype of the L-type calcium channel (Ca(v)1.3). In the present investigation, we have studied its distribution and cellular localization in the cat spinal cord by light and electron microscopic immunohistochemistry. The results show that Ca(v)1.3-like immunoreactivity is widely distributed in all segments of the spinal cord but that the distribution in the different laminae of the spinal gray matter varies, with the highest density of labeled neurons in lamina IX and the lowest in lamina II. The labeling intensity was highest in neuronal somata, but a certain length of the proximal dendrite was also labeled. Some neuronal groups exhibited a particularly dense labeling; these include the lateral motoneuronal group in the cervical and the lumbar enlargements and the phrenic nucleus in cervical, Clarke's nucleus in lower thoracic and upper lumbar, and Onuf's nucleus in upper sacral segments. At the ultrastructural level, Ca(v)1.3-immunoreactive products were found in neuronal somata and dendrites of different sizes. In the soma, they were predominantly associated with the rough endoplasmic reticulum but some also with the plasma membrane. In dendrites, they were associated with both intracellular organelles, including microtubules and microchondria, and the plasma membrane. These results indicate that significant proportions of the neurons in cat spinal cord, including projection neurons, interneurons, and motoneurons, are endowed with ion channels that subserve persistent inward currents and act to amplify synaptic input signals.
|
|
| 18239. |
- Zhang, Ping, et al.
(författare)
-
Dietary Sphingomyelin Inhibits Colonic Tumorigenesis with an Up-regulation of Alkaline Sphingomyelinase Expression in ICR Mice
- 2008
-
Ingår i: Anticancer research. - 1791-7530. ; 28:6A, s. 3631-3635
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Sphingomyelin (SM) hydrolysis generates biologically active products regulating cell growth, differentiation and apoptosis. Dietary SM has been found to inhibit colonic tumorigenesis. Alkaline sphingomyelinase (alk-SMase) is the key enzyme responsible for sphingomyelin digestion in the gut. Whether or not dietary sphingomyelin affects alk-SMase expression was examined in a colon cancer animal model. Materials and Methods: Imprinting control region (ICR) mice were injected with 1,2-dimethylhydrazine (DMH) and then fed a diet with or without SM (0.5 g/kg in diet) for 22 weeks. The colonic tumorigenesis and alk-SMase activity were determined and alk-SMase expression was examined by Western blot and PCR. Results: Dietary SM inhibited the tumorigenesis and increased the alk-SMase activity in the colon by 65%. The increased activity was associated with increased enzyme protein and mRNA expression. No changes of acid and neutral sphingomyelinase activities were found. Conclusion: Long-term supplementation with dietary sphingomyelin up-regulates colonic alk-SMase expression, which may contribute to the inhibitory effects of sphingomyelin against colonic carcinogenesis.
|
|
| 18240. |
|
|
