Approximately unitarily equivalent morphisms and inductive limitC*-algebras

It is shown that two unital *-homomorphisms from a commutativeC*-algebraC(X) to a unitalC*-algebraB are stably approximately unitarily equivalent if and only if they have the same class in the quotient of the Kasparov groupKK(C(X),B) by the closure of zero. A suitable generalization of this result is used to prove a classification result for certain inductive limitC*-algebrasThis research was partially supported by NSF grant DMS-9303361     

Synthesis,Biological Evaluation,and Docking Studies of Antagonistic Hydroxylated Arecaidine Esters Targeting mAChRs

The muscarinic acetylcholine receptor family is a highly sought-after target in drug and molecular imaging discovery efforts aimed at neurological disorders. Hampered by the structural similarity of the five subtypes’ orthosteric binding pockets, these efforts largely failed to deliver subtype-selective ligands. Building on our recent successes with arecaidine-derived ligands targeting M₁, herein we report the synthesis of a related series of 11 hydroxylated arecaidine esters. Their physicochemical property profiles, expressed in terms of their computationally calculated CNS MPO scores and HPLC-logD values, point towards blood–brain barrier permeability. By means of a competitive radioligand binding assay, the binding affinity values towards each of the individual human mAChR subtypes hM₁–hM₅ were determined. The most promising compound of this series 17b was shown to have a binding constant towards hM₁ in the single-digit nanomolar region (5.5 nM). Similar to our previously reported arecaidine-derived esters, the entire series was shown to act as hM1R antagonists in a calcium flux assay. Overall, this study greatly expanded our understanding of this recurring scaffolds’ structure–activity relationship and will guide the development towards highly selective mAChRs ligands.     

Are signal intensity and homogeneity useful parameters for distinguishing between benign and malignant soft tissue masses on MR images?: Objective evaluation by means of texture analysis

Objectives

To objectively identify possible differences in the signal characteristics of benign and malignant soft tissue masses (STM) on magnetic resonance (MR) images by means of texture analysis and to determine the value of these differences for computer-assisted lesion classification.

Method

Fifty-eight patients with histologically proven STM (benign, n=30; malignant, n=28) were included. STM texture was analyzed on routine T1-weighted, T2-weighted and short tau inversion recovery (STIR) images obtained with heterogeneous acquisition protocols. Fisher coefficients (F) and the probability of classification error and average correlation coefficients (POE+ACC) were calculated to identify the most discriminative texture features for separation of benign and malignant STM. F>1 indicated adequate discriminative power of texture features. Based on the texture features, computer-assisted classification of the STM by means of k-nearest-neighbor (k-NN) and artificial neural network (ANN) classification was performed, and accuracy, sensitivity and specificity were calculated.

Results

Discriminative power was only adequate for two texture features, derived from the gray-level histogram of the STIR images (first and 10th gray-level percentiles). Accordingly, the best results of STM classification were achieved using texture information from STIR images, with an accuracy of 75.0% (sensitivity, 71.4%; specificity, 78.3%) for the k-NN classifier, and an accuracy of 90.5% (sensitivity, 91.1%; specificity, 90.0%) for the ANN classifier.

Conclusion

Texture analysis revealed only small differences in the signal characteristics of benign and malignant STM on routine MR images. Computer-assisted pattern recognition algorithms may aid in the characterization of STM, but more data is necessary to confirm their clinical value.     

Coherent neural oscillations induced by weak synaptic noise

Nonlinear Dynamics - We analyze the effect of synaptic noise on the dynamics of the FitzHugh–Nagumo (FHN) neuron model. In our deterministic parameter regime, a limit cycle solution cannot...     

The nanotechnology patent thicket revisited

Despite all predictions and promises, nanotechnology still seems to be more of an emerging science than a fully fledged revolution. More often than not, the patent system is blamed for this, supposedly tangling up nanotechnology in an impenetrable thicket of exclusionary rights instead of setting it free. Drawing on methods of complex network analysis, we provide empirical evidence suggesting that, at least in Europe, there is actually no patent thicket present in nanotechnology. Yet, the situation appears to be different in the USA.     

TROSY-based z-exchange spectroscopy: application to the determination of the activation energy for intermolecular protein translocation between specific sites on different DNA molecules

A two-dimensional TROSY-based z-exchange 1H-15N correlation experiment for the quantitative analysis of kinetic processes in the slow exchange regime is presented. The pulse scheme converts the product operator terms Nz into 2NzHz and 2NzHz into -Nz in the middle of the z-mixing period, thereby suppressing the buildup of spurious semi-TROSY peaks arising from the different relaxation rates for the Nz and 2NzHz terms and simplifying the behavior of longitudinal magnetization for an exchanging system during the mixing period. Theoretical considerations and experimental data demonstrate that the TROSY-based z-exchange experiment permits quantitative determination of rate constants using the same procedure as that for the conventional non-TROSY 15Nz-exchange experiment. Line narrowing as a consequence of the use of the TROSY principle makes the method particularly suitable for kinetic studies at low temperature, thereby permitting activation energies to be extracted from data acquired over a wider temperature range. We applied this method to the investigation of the process whereby the HoxD9 homeodomain translocates between specific target sites on different DNA molecules via a direct transfer mechanism without going through the intermediary of free protein. The activation enthalpy for intermolecular translocation was determined to be 17 kcal/mol.     

13-tungstoborate stabilized by an organostannoxane hexamer

The novel dimethyltin-containing polyanion [{(CH3)2Sn}6(OH)2O2(H2BW13O46)2]12- (1) is composed of two [H2BW13O46]9- clusters linked by an unprecedented planar, hexameric [{(CH3)2Sn}6(OH)2O2]8+ organostannoxane moiety, representing the first X-ray structural characterization of a molecular hybrid organic-inorganic tungstoborate and of the elusive [HnBW13O46](11-n)- species.     

Steiner transitive-closure spanners of low-dimensional posets

Given a directed graph G=(V, E) and an integer k ≥ 1, a k-transitive-closure spanner (k-TC-spanner) of G is a directed graph H=(V, E _H ) that has (1) the same transitive closure as G and (2) diameter at most k. In some applications, the shortcut paths added to the graph in order to obtain small diameter can use Steiner vertices, that is, vertices not in the original graph G. The resulting spanner is called a Steiner transitive-closure spanner (Steiner TC-spanner). Motivated by applications to property reconstruction and access control hierarchies, we concentrate on Steiner TC-spanners of directed acyclic graphs or, equivalently, partially ordered sets. In these applications, the goal is to find a sparsest Steiner k-TC-spanner of a poset G for a given k and G. The focus of this paper is the relationship between the dimension of a poset and the size of its sparsest Steiner TC-spanner. The dimension of a poset G is the smallest d such that G can be embedded into a d-dimensional directed hypergrid via an order-preserving embedding. We present a nearly tight lower bound on the size of Steiner 2-TC-spanners of d- dimensional directed hypergrids. It implies better lower bounds on the complexity of local reconstructors of monotone functions and functions with small Lipschitz constant. The lower bound is derived from an explicit dual solution to a linear programming relaxation of the Steiner 2-TC-spanner problem. We also give an efficient construction of Steiner 2-TC-spanners, of size matching the lower bound, for all low-dimensional posets. Finally, we present a lower bound on the size of Steiner k-TC-spanners of d-dimensional posets. It shows that the best-known construction, due to De Santis et al., cannot be improved significantly.