Surfaces with zero Lefschetz cycles

We study a number of conditions equivalent to homology to0 of vanishing cycles on a non-singular complex projective surface, and we classify such surfaces.Translated from Matematicheskie Zametki, Vol. 13, No. 6, pp. 869–880, June, 1973.     

Switching the Inhibitor-Enzyme Recognition Profile via Chimeric Carbonic Anhydrase XII

A key part of the optimization of small molecules in pharmaceutical inhibitor development is to vary the molecular design to enhance complementarity of chemical features of the compound with the positioning of amino acids in the active site of a target enzyme. Typically this involves iterations of synthesis, to modify the compound, and biophysical assay, to assess the outcomes. Selective targeting of the anti-cancer carbonic anhydrase isoform XII (CA XII), this process is challenging because the overall fold is very similar across the twelve CA isoforms. To enhance drug development for CA XII we used a reverse engineering approach where mutation of the key six amino acids in the active site of human CA XII into the CA II isoform was performed to provide a protein chimera (chCA XII) which is amenable to structure-based compound optimization. Through determination of structural detail and affinity measurement of the interaction with over 60 compounds we observed that the compounds that bound CA XII more strongly than CA II, switched their preference and bound more strongly to the engineered chimera, chCA XII, based on CA II, but containing the 6 key amino acids from CA XII, behaved as CA XII in its compound recognition profile. The structures of the compounds in the chimeric active site also resembled those determined for complexes with CA XII, hence validating this protein engineering approach in the development of new inhibitors.     

The role of magnetization compensation point for efficient ultrafast control of magnetization in Gd<Subscript>24</Subscript>Fe<Subscript>66.5</Subscript>Co<Subscript>9.5</Subscript> alloy

The ability of a femtosecond laser pulse to manipulate and reverse the magnetization in a ferrimagnetic Gd₂₄Fe_66.5Co_9.5 thin film was studied experimentally as a function of temperature. For a fixed energy of the laser pulse, the dynamics of magnetization showed different behavior depending on whether the sample temperature was below or above the magnetization compensation point (T _M ). The conditions for full ultrafast demagnetization and magnetization reversal were easily achieved below T _M , while the same laser excitation caused just 50% demagnetization above T _M . This interesting change in magnetization dynamics is qualitatively explained in terms of effective changes in the magnitudes of magnetizations of atomic sublattices.     

Establishing a Flow Process to Coumarin‐8‐Carbaldehydes as Important Synthetic Scaffolds

Despite their usefulness as fluorophores and synthetic precursors, efficient and reliable routes to coumarin‐8‐carbaldehydes are lacking. We describe here a high‐yielding continuous flow synthesis that requires no manual intermediate purification or work‐up, giving access to multigram quantities of the aldehyde product.     

The Bergman‐Shelah preorder on transformation semigroups

Let $\mathbb {N}^\mathbb {N}Let $\mathbb {N}^\mathbb {N}$ be the semigroup of all mappings on the natural numbers $\mathbb {N}$, and let U and V be subsets of $\mathbb {N}^\mathbb {N}$. We write U?V if there exists a countable subset C of $\mathbb {N}^\mathbb {N}$ such that U is contained in the subsemigroup generated by V and C. We give several results about the structure of the preorder ?. In particular, we show that a certain statement about this preorder is equivalent to the Continuum Hypothesis. The preorder ? is analogous to one introduced by Bergman and Shelah on subgroups of the symmetric group on $\mathbb {N}$. The results in this paper suggest that the preorder on subsemigroups of $\mathbb {N}^\mathbb {N}$ is much more complicated than that on subgroups of the symmetric group.     

Role of magnetic circular dichroism in all-optical magnetic recording

Using magneto-optical microscopy in combination with ellipsometry measurements, we show that all-optical switching with polarized femtosecond laser pulses in ferrimagnetic GdFeCo is subjected to a threshold fluence absorbed in the magnetic layer, independent of either the excitation wavelength or the polarization of the laser pulse. Furthermore, we present a quantitative explanation of the intensity window in which all-optical helicity-dependent switching (AO-HDS) occurs, based on magnetic circular dichroism. This explanation is consistent with all the experimental findings on AO-HDS so far, varying from single- to multiple-shot experiments. The presented results give a solid understanding of the origin of AO-HDS, and give novel insights into the physics of ultrafast, laser controlled magnetism.     

A sensitive reaction for dilute cholesterol determinations

A sensitive reaction for the peroxidase-coupled sequence of the determination of a dilute total cholesterol mixture of free and esterified forms is described. Substitution of a chlorinated auxochrome of phenol made water soluble by sulfonation through a synthetic procedure previously described created a severalfold enhancement factor which magnified considerably the sensitivity of one equilibrium reaction over the other. This enabled the determination of dilute cholesterol solutions to be carried out with high absorbance signals across the range of 0.0–10.0 mg/liter (0–0.0259 mmol/liter) of cholesterol, a range which includes and exceeds the normal values one would encounter in dilute solutions such as cerebrospinal fluid. Important potential interference factors including increased protein concentrations and calcium and magnesium were considered and studied. The formidable interacting compound, bilirubin, which is competitive with the 4-aminoantipyrene and sodium 2-hydroxy-3, 5-dichlorobenzenesulfonate mixture in the peroxidase sequence was also studied, its interference characteristics were determined and an alternative methodology suggested for obviating this perturbing effect. It is believed that the simple substitution of the auxochrome derivative is a useful contribution not only here but in studies presently ongoing involving needed sensitivity for cholesterol fractions which are considerably lower than the serum total cholesterol concentrations most commonly determined.     

One-loop scalar field contributions to graviton-graviton scattering and helicity non-conservation in quantum gravity

We present and discuss the helicity amplitudes for graviton-graviton scattering via a loop of massless scalars. The amplitudes have the expected analytic structure but do not conserve helicity. We prove that as a consequence helicity is not conserved in pure quantum gravity either and the helicity flip amplitudes are given by two times the scalar loop contributions. Implications for the higher-loop renormalizability of quantum gravity are discussed.