5941 research outputs found
Sort by
First-passage time: Lattice versus continuum
No full textRestricted Access.The well known approach, based on Schrödinger's integral equation, to the problem of calculating the first-passage probability density in time for classical diffusion on a continuum is revisited for the case of diffusion by hopping on a discrete lattice. It turns out that a certain boundary condition central to solving the integral equation, invoked first by Schrödinger and then by others on the basis of a physical argument, needs to be modified for the discrete case. In fact, the required boundary condition turns out to be determined entirely by the normalization condition for the first-passage probability density. An explicit analytical expression is derived for the first-passage density for a three-site problem modeling escape over a barrier. The related quantum first-passage problem is also commented upon briefly
Single-pulse analysis of PSR B1133+16 at 8.35 GHz and carousel circulation time
No full textRestricted AccessA successful attempt has been made to analyse about 6000 single pulses of PSR B1133+16 obtained with the 100-m Effelsberg radio telescope. The high-resolution (60 μs) data were taken at a frequency of 8.35 GHz with a bandwidth of 1.1 GHz. In order to examine the pulse-to-pulse intensity modulations, we performed both longitude- and harmonic-resolved fluctuation spectral analysis. We identified the low-frequency feature associated with an amplitude modulation at , which can be interpreted as the circulation time P4≃ 30 P1 of the underlying subbeam carousel model. Despite the erratic nature of this pulsar, we also found evidence of periodic pseudo-nulls with P4= 28.44 P1. This is exactly the value at which Herfindal & Rankin found periodic pseudo-nulls in their 327 MHz data. We thus believe that this is the actual carousel circulation time in PSR B1133+16, particularly during orderly circulation
Studies on Langmuir monolayer of tricycloquinazoline based disk-shaped liquid crystal molecules
No full textRestricted Access.The assembly of disk-shaped molecules on surfaces has drawn considerable attention because of their unique electronic and optical properties. We have studied the monolayer of the amphiphilic tricycloquinazoline (AmTCQ) based disk-shaped molecules at the air–water and air–solid interfaces. The AmTCQ molecules form a stable Langmuir monolayer at the air–water interface. The monolayer exhibits gas phase, low density liquid (L1) phase, and high density liquid (L12) phase. In L1 phase, the molecules prefer face-on conformation with their flexible side-chain being interdigitated with the neighboring molecules. Interestingly, the molecular conformations in L12 phase were found to be both the face-on and edge-on. The structure of the aggregates of the molecules on a surface can be influenced by the intermolecular and molecule–substrate interactions. The deficiency in π-electrons of the AmTCQ molecule may lead to a weak intermolecular interaction. The observation of both the conformations of the molecules in L12 phase can be attributed to the weak intermolecular interaction
Modulated phases of phospholipid bilayers induced by tocopherols
No full textRestricted Access.The influence of α-, γ‐ and δ-tocopherols on the structure and phase behavior of dipalmitoyl phosphatidylcholine (DPPC) bilayers has been determined from X-ray diffraction studies on oriented multilayers. In all the three cases the main-transition temperature (Tm) of DPPC was found to decrease with increasing tocopherol concentration up to around 25 mol%. Beyond this the main transition is suppressed in the case of γ‐tocopherol, whereas Tm becomes insensitive to composition in the other two cases. The pre-transition is found to be suppressed over a narrow tocopherol concentration range between 7.5 and 10 mol% in DPPC‐γ-tocopherol and DPPC-δ‐tocopherol bilayers, and the ripple phase occurs down to the lowest temperature studied. In all the three cases a modulated phase is observed above a tocopherol concentration of about 10 mol%, which is similar to the Pβ phase reported in DPPC–cholesterol bilayers. This phase is found to occur even in excess water conditions at lower tocopherol concentrations, and consists of bilayers with periodic height modulation. These results indicate the ability of tocopherols to induce local curvature in membranes, which could be important for some of their biological function
Methyl 4-benzyloxy-2-hydroxybenzoate
No full textopen Access.In the title compound, C15H14O4, the dihedral angle between the benzene rings is 67.18 (8) . The Ca—Cm—O—Ca (a = aromatic and m = methylene) torsion angle is 172.6 (3) and an intramolecular O—H O hydrogen bond generates an S(6) ring. In the crystal, molecules are linked by C—H O hydrogen bonds into zigzag chains propagating in [001] and C—H interactions also occu
Hetero-epitaxial Growth of Cubic La(Sr)MnO3 on Hexagonal ZnO, in-plane orientations of La(Sr)MnO3 (001), (110), and (111) Phases
No full textRestricted Access.Hexagonal ZnO was grown on a hexagonal (001) sapphire substrate. Then cubic La(Sr)MnO3 (LSMO) was grown on a ZnO underlayer by ion beam sputtering at various substrate temperatures to obtain double-layers of LSMO/ZnO and to investigate hetero-epitaxial orientation growth. Out-of-plane (001)-oriented ZnO was grown with an in-plane orientation of [10\bar{1}0](001)ZnO \parallel [11\bar{2}0](001)sapphire (B-mode). Three phases of LSMO with out-of-plane (001), (110), and (111) orientations were grown on (001) ZnO generally. However, each single phase of LSMO could be grown only by controlling the deposition conditions. We achieved the in-plane orientation growth of LSMO, [110](001)LSMO \parallel [10\bar{1}0](001)ZnO (B-mode), [1\bar{1}0](110)LSMO \parallel [10\bar{1}0](001)ZnO (A-mode), and [1\bar{1}0](111)LSMO \parallel [11\bar{2}0](001)ZnO (B-mode). The A-mode is defined as the mode in which both in-plane fundamental axes are parallel. The B-mode entails no parallel axes. The LSMO(001)- and (110)-grains have three equivalent in-plane domains, and the LSMO(111)-grain has a single domain. Lattice matching calculation can be used to partially interpret the orientation growth