An example of an SL2-Hilbert scheme with multiplicities

In [AB05], Alexeev and Brion have introduced the notion of invariant Hilbert schemes. We determine the invariant Hilbert scheme of the zero fibre of the moment map of an action of SL₂ on ( \mathbbC² ) ^?6 {\left( {{\mathbb{C}^2}} \right)^{ \oplus 6}} as one of the first examples of invariant Hilbert schemes with multiplicities. While doing this, we present a general procedure for realizing these calculations. We also consider questions of smoothness and connectedness and thereby show that our Hilbert scheme gives a resolution of singularities of the symplectic reduction of the action.     

Antibunching in the emission of a single tetrachromophoric dendritic system

The photophysics of a dendrimer containing four chromophores are investigated at the single-molecule level. First, the multichromophoric character of single dendrimers' absorption is probed by modulating the linear polarization of the excitation beam. Subsequently, using circular polarization, the same dendrimers are excited, and their fluorescence transients are recorded. Using pulsed excitation in combination with the classical Hanbury-Brown and Twiss coincidence setup the presented data demonstrate that efficient singlet-singlet annihilation ensures that always only one photon is emitted even when several excitations are generated in an individual multichromophoric molecule.     

First measurement of the double spin asymmetry in (-->)e(-->)p-->e(prime)pi(+)n in the resonance region

The double spin asymmetry in the (-->)e(-->)p --> e(prime)pi(+)n reaction has been measured for the first time in the resonance region for four-momentum transfer Q2 = 0.35-1.5 GeV(2). Data were taken at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH3 target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with Q(2) of the helicity asymmetry A1 for the F(15)(1680) resonance than expected from the analysis of the unpolarized data.     

A study of N by means of the B(α, α)B reaction

The ¹¹B(α, α)¹¹B cross section has been measured as a function of energy and angle for bombarding energies from 4 to 8 MeV. Many resonances are observed. The data from 4 to 5 MeV were fitted using an R-matrix formalism with background phase shifts evolved from an optical-model potential. The three levels in ¹⁵N resulting from this analysis fit into the APCETS scheme for ¹⁵N.     

Der Druckeinflu? auf die Bildung von Hetero-Excimeren. 2. Mitt. Verschiedene Donor-Akzentor-Systeme in n-Hexan

Ohne Zusammenfassung     

A quantitative interpretation of the magnetic field effect on hyperfine-coupling-induced triplet fromation from radical ion pairs

Experimentally determined B_1/2 values characterizing the magnetic field dependence of molecular triplet production from radical ion pairs originating from photoinduced electron transfer are compared with semi-empirical values obtained according to B_1/2(hfi) = 2(B₁² + B₂²)/(B₁ + B₂) from the root-mean-square values for the hyperfine coupling of the two radicals, B₁ and B₂. The very good agreement is discussed.     

Viscoelastic shear properties of in vivo breast lesions measured by MR elastography

Elastography is a technique to assess the viscoelastic properties of tissue by measuring an acoustic wave propagating though the object. Here, the technique is applied in the course of standard MR mammography to 15 patients with different pathologies (six breast cancer cases, six fibroadenoma cases and three mastopathy cases). Low-frequency mechanical waves are coupled longitudinally into the tissue in order to obtain sufficient wave amplitude throughout the entire breast. This leads to the presence of a substantial fraction of compressional waves, which contribute to the total displacement field. It is shown theoretically that the correct evaluation of these contributions from the compressional wave is rather difficult due to the almost incompressible nature of tissue. To overcome this problem, it is proposed to apply the curl-operator to the measured displacement field in order to completely remove contributions from the compressional wave. Results from simulations and a breast phantom demonstrate the feasibility of the technique. The in vivo results show a good separation between breast cancer and benign fibroadenoma utilizing the shear modulus. Breast cancer appears on average 2.2 (P<.001) times stiffer. All breast cancer cases showed a good delineation to the surrounding breast tissue with an average elevation of a factor of 3.3 (P< 1.4 x 10(-6)). The results as obtained for the shear viscosity do not indicate to be useful for separating benign from malignant lesions.     

Self-poisoning of crystal nuclei in hard-rod liquids

We report a Monte Carlo study of the pathway for crystal nucleation in a fluid of hard, colloidal rods. In the earliest stages of nucleation, a lamellar crystallite forms. Subsequent thickening of this lamella is hampered by the fact that the top and bottom surfaces of this crystallite are preferentially covered by rods that align parallel to the surface. As a consequence, subsequent growth of individual crystals is stunted. Experimental evidence for such stunted crystal growth has recently been reported by Maeda and Maeda in experiments on suspensions of colloidal rods [Phys. Rev. Lett. 90, 018303 (2003)]]. The simulations suggest that, in experiments, the growth of multilayer colloidal crystals can be selectively enhanced by the application of an external aligning field.