Convenient synthesis of nucleoside and isonucleoside analogues

[reaction: see text]. A very simple methodology to stereoselectively achieve tricyclic isonucleosides (nucleobase = thymine, uracil, and 5-fluoruracil) and 3'-C-branched nucleosides (nucleobase = theophylline) was performed by means of a DBU-mediated addition process using a readily available 2-bromo sugar. The mechanism for these transformations implies the loss of both substituents at C-2 and C-3 on the sugar moiety, and although it seems that DBU is probably involved, its involvement has not yet been ascertained. Cytosine did not react under these conditions.     

The triviality of continuous multipliers for the real line

It is proved without resort to calculus methods that every continuous group multiplier for R can be reduced to the identity by a continuous remultiplication. The method introduced may generalize to infinitedimensional Abelian groups such as occur in analyzing the projective representations of the Bondi-Metzner-Sachs (BMS) group.     

The synthesis of thienocycloheptenoindoles

A synthesis of the methylthieno[3,2-c]cyclohepteno[b]indole 7 from 2-methylthieno[3,2-b]cycloheptanone 3 is described. Unsuccessful attempts to prepare the isomeric thienocycloheptenoindole system present in formula 2 , from the dihydrobenzothiophenone 8 , and from derivatives of 5-(2-thienyl)-4-oxopentanoic acid, 17 and 18 , and from N-benzylcycloheptindol-1-one 22 were unsuccessful. The preparation of 4,5-dihydro-2-phenyl-1-thienylmethyl-3H-pyridazin-3-one 20 and of the 5-aminopyrazole 21 are reported.     

Lossless Medical Image Compression by Using Difference Transform

This paper introduces a new method of compressing digital images by using the Difference Transform applied in medical imaging. The Difference Transform algorithm performs the decorrelation process of image data, and in this way improves the encoding process, achieving a file with a smaller size than the original. The proposed method proves to be competitive and in many cases better than the standards used for medical images such as TIFF or PNG. In addition, the Difference Transform can replace other transforms like Cosine or Wavelet.     

Wavefront sensing with critical sampling

Different types of nonredundant sampling patterns are shown to guarantee completeness of the basis formed by the sampled partial derivatives of Zernike polynomials, commonly used to reconstruct the wavefront from its slopes (wavefront sensing). In the ideal noise-free case, this enables one to recover double the number of modes J than sampling points I (critical sampling J=2I). With real data, noise amplification makes the optimal number of modes lower I相似文献   

Optical loss measurements in femtosecond laser written waveguides in glass

The optical loss is an important parameter for waveguides used in integrated optics. We measured the optical loss in waveguides written in silicate glass slides with high repetition-rate (MHz) femtosecond laser pulses. The average transmission loss of straight waveguides is about 0.3 dB/mm at a wavelength of 633 nm and 0.05 dB/mm at a wavelength of 1.55 μm. The loss is not polarization dependent and the waveguides allow a minimum bending radius of 36 mm without additional loss. The average numerical aperture of the waveguides is 0.065 at a wavelength of 633 nm and 0.045 at a wavelength of 1.55 μm. In straight waveguides more than 90% of the transmission loss is due to scattering.     

Characteristic properties of the conical Mueller matrix

We present results of mathematical relations existing between the Mueller matrix obtained for an in-plane of incidence scattering geometry (plane Mueller matrix, PMM) and the Mueller matrix obtained for an out-the-plane of incidence scattering geometry (conical Mueller matrix, CMM), for light scattered from a rough surface. We obtain a similarity relation between the CMM and the PMM for one- (1-D) and for two-dimensional (2-D) surfaces. This similarity relation implies that the PMM and the CMM have the same determinant, trace and eigenvalues for 1-D and 2-D surfaces, respectively. We can say that measurements made in the conical geometry are “Similarity Equivalent” to those in the in-plane geometry for both kind of surfaces, respectively.     

Optimal bounds for ratios of eigenvalues of one-dimensional Schrödinger operators with Dirichlet boundary conditions and positive potentials

Consider the Schrödinger equation –u+V(x)u=u on the intervalI, whereV(x)0 forxI and where Dirichlet boundary conditions are imposed at the endpoints ofI. We prove the optimal bound

A sum-over-histories account of an EPR(B) experiment

We analyze a variant of the EPRB experiment within a framework for quantum mechanics that rests on a radical interpretation of the sum over histories. Within this framework, reality is (just as classically) a single history, e.g. a definite collection of particles undergoing definite motions; and quantum dynamics appears as a kind of stochastic law of motion for that history, a law formulated in terms of non-classical probability-amplitudes. No state vectors enter this framework, and their attendant nonlocality is therefore absent as well.1. That is, before pair creations and annihilations were discovered. (The electronic and nuclear spins might also be regarded as new aspects of their kinematics. But perhaps spin is better construed, within the sum-over-histories framework, as a quality of a more dynamical character, namely as a generalized sort of probability-amplitude.)2. A possible escape would be the so-called Everett interpretation, in which the collapse never occurs, but its effects are supposed to be recovered via a more careful analysis of closed systems in which measurement-like processes take place. Among other things, this approach tends to lead either to the view that nothing really happens [1] or to the view that everything really happens [2] (which perhaps is not that different from the former view).3. For example, the rule, collapse occurs along the past light cone (in the Heisenberg picture), appears to be consistent.4. And Bell's inequality shows thatany theory formulated in terms of an instantaneous state evolving in time would encounter the same trouble. Indeed, the trouble shows up even more glaringly if one adapts Bell's argument to spin-1 systems, using the results of Kochen and Specker[10]. In order to use the Kochen-Specker results in the EPR manner one needs a scheme for measuring the relevant observables, but this can be accomplished by means of suitably concatenated Stern-Gerlach analyzers with recombining beams [13]. Then, as Allen Stairs has pointed out [14], even the perfect correlations become impossible to reproduce, and no reference to probability theory is needed to establish a contradiction with locality. Recently, an analogous experiment using three spin 1/2 particles instead of two spin 1 particles has also been given [15].5. No technical problem obstructs an extension to fermionic fields (indeed the functional integral formalism for Quantum Field Theory is probably the most popular at present), but the realistic interpretation of the individual histories seems to get lost. One way out would be if all fermions were composites or collective excitations of fields quantized according to bosonic commutation relations. Another would be if the particle formulation were taken as basic, with the complementary field formulation being merely a mathematical artifice (at least for fermions).6. In the approach of Gell-Mann-Hartle and Griffiths for example, only a small subset of the possible partitions is granted meaning, in such a way that all interference terms are suppressed and quantum probabilities reduce to classical ones.7. In stating these rules we consider an idealized situation in which the spatio-temporal indeterminacy of particle-locationwithin a given one of our trajectories is ignored; or if you prefer, you can take the experiment as only a Gedanken one affording a simplified illustration of how EPR-like correlations are understood within the sum-over-histories framework. In this connection recall also that the semiclassical propagator is in fact exact for a free particle.8. This can be interpreted either as part of the specification of the initial conditions, or (as suggested by a referee) merely as an example of relativization of probabilities.9. Thus a state vector may be defined as an equivalence-class of sets of partial histories.10. One such generalization applies to open systems, for example to a particle in contact with a heat reservoir. For this example see [11], wherein the two-way path formalism of §5 above is used, and the influence of the reservoir results in an effective dynamics for the particle in which the forward and backward portions of its world-line are coupled to each other by a certain interaction term in the amplitude. In this type of situation a density-operator (though not a state vector ) can still be introduced, but it no longer summarizes all the relevant information about the past (and correspondingly its evolution lacks the Markov property that(t + dt) is determined by(t) alone). For quantum gravity, it may be that not even such a non-Markov will be exactly definable, and only the global probabilities themselves will make sense.11. Ironically it is just this property of the amplitudes which, as mentioned above, makes possible the introduction of the state vectors whose collapse then introduces such a strong appearance ofnonlocality into the theory.