Chiral Ligand?Induced Circular Dichroism in Excitonic Absorption of Colloidal Quantum Dots

A range of unique properties have been extensively studied in colloidal semiconductor nanocrystals (quantum dots, QDs). The possibility to manipulate the properties of these systems by controlling size and composition is attractive for many different applications, as well as for fundamental studies. Recently, the properties of chirality and chiroptical activity induced by surface ligands at QDs were considered. It was shown that chiroptical activity can be induced in the exciton transitions of quantum dots by capping them with chiral molecules. In this work, chiroptical spectroscopy (mainly circular dichroism) is used to study induced effects in CdS, CdSe and ZnSe QD systems. Some fundamental differences are encountered between CdS or CdSe samples and ZnSe samples. The results are analyzed to account for the mechanism of induction of chiroptical activity in the inorganic core by chiral capping molecules. Two electronic mechanisms of interaction are considered and discussed in light of the results. It is also suggested that chiroptical spectroscopy might serve as an efficient tool to characterize electronic (or electron-hole) level spectra of nanocrystal systems by analyzing circular dichroism intensity and lineshape.     

Deep Inside Cucurbiturils: Physical Properties and Volumes of their Inner Cavity Determine the Hydrophobic Driving Force for Host–Guest Complexation

Cucurbit[n]urils (CBn) bind guest molecules through a combination of electrostatic interactions with the carbonyl rims and hydrophobic interactions with the inner cavity. Investigations with solvatochromic probes in CB7 reveal that the polarity of the cavity resembles that of alcohols (e.g., n-octanol), while its polarizability (P=0.12) and apparent refractive index (n_D=1.10±0.12) are extremely low, close to the gas phase. The calculated molecular quadrupole moments of CBs are extremely large (Θ_zz=−120 to −340 Buckingham). A survey of reported binding constants of neutral guests and hydrophobic residues that form 1 : 1 inclusion complexes with CB6, reveals a preferential inclusion of C3–C5 residues in its cavity. The largest guests which show non-negligible binding contain 7 heavy atoms (excluding hydrogen). For CB7, the strongest binding is observed for guests with adamantyl (10 heavy atoms) and ferrocenyl groups (11 heavy atoms), while the largest guests known to be complexed are carborane and the adduct of two pyridine derivatives (12 heavy atoms). The evaluation of different volumes shows that the most meaningful cavity, namely that responsible for binding of hydrophobic residues, is confined by the planes through the oxygen carbonyls. The volume of this inner cavity follows the formula V/ų=68+62(n−5)+12.5(n−5)², affording representative cavity volumes of 68 ų for CB5, 142 ų for CB6, 242 ų for CB7, and 367 ų for CB8. The volume of the 2 bond dipole regions is comparably smaller, amounting, for example, to 2×35 ų for CB6. The analysis of packing coefficients for representative sets of known guests with clearly defined hydrophobic binding motifs reveals average values of 47 % for CB5, 58 % for CB6, 52 % for CB7, and 53 % for CB8, which are well in line with the preferred packing (“55 % solution”, see S. Mecozzi, J. Rebek, Chem. Eur. J. 1998 , 4, 1016–1022) in related supramolecular host–guest assemblies. The driving force for binding of hydrophobic guests and residues by CBs is interpreted in terms of the unimportance of dispersion interactions (owing to the low polarizability of their cavity) and the dominance of classical and nonclassical hydrophobic effects related to the removal of very-high-energy water molecules (2 for CB5, 4 for CB6, 8 for CB7, and 12 for CB8) from the cavity.     

A scheduling framework for large-scale,parallel, and topology-aware applications

Scheduling of large-scale, distributed topology-aware applications requires that not only the properties of the requested machines be considered, but also the properties of the machines’ interconnections. This requirement severely complicates the scheduling process, as even a matching between a single multi-processor task and available machines in a single time slot becomes an NP-complete problem with no polynomial approximation. In this paper we propose a complete scheduling framework for multi-cluster, heterogeneous environments that provides, in practice, an efficient solution for the scheduling of topology-aware applications. The proposed framework is very flexible as it is composed of pluggable components and can be easily configured to support a variety of scheduling policies. We also describe three novel scheduling and coallocation algorithms that were developed and plugged into the framework. The proposed scheduling framework was integrated into the QosCosGrid ¹ system, where it is used as the main decision-making module.     

Compressed Genotyping

Over the past three decades we have steadily increased our knowledge on the genetic basis of many severe disorders. Nevertheless, there are still great challenges in applying this knowledge routinely in the clinic, mainly due to the relatively tedious and expensive process of genotyping. Since the genetic variations that underlie the disorders are relatively rare in the population, they can be thought of as a sparse signal. Using methods and ideas from compressed sensing and group testing, we have developed a cost-effective genotyping protocol to detect carriers for severe genetic disorders. In particular, we have adapted our scheme to a recently developed class of high throughput DNA sequencing technologies. The mathematical framework presented here has some important distinctions from the 'traditional' compressed sensing and group testing frameworks in order to address biological and technical constraints of our setting.     

Scheduling with a common due-window: Polynomially solvable cases

The single machine scheduling problem to minimize maximum weighted absolute deviations of job completion times from a common due-date, is known to be NP-hard. However, two special cases have been shown to have polynomial time solutions: the case of unit processing time jobs, and the case of due-date assignment for a given job sequence. We extend both cases to a setting of a common due-window. We show that the unit-job problem includes 12 different sub-cases, depending on the size and location of the (given) due-window. Scheduling and due-window assignment for a given job sequence is solved for a single machine, for parallel identical machines and for flow-shops. For each of the above cases, an appropriate special-structured linear program is presented.     

Ethanol steam reforming over rhodium and cobalt-based catalysts: Effect of the support

The effect of support on the properties of rhodium and cobalt-based catalysts for ethanol steam reforming was studied in this work, by comparing the use of magnesia, alumina and Mg–Al oxide (obtained from hydrotalcite) as supports. It was found that metallic rhodium particles with around 2.4–2.6 nm were formed on all supports, but Mg–Al oxide led to the narrowest particles size distribution; cobalt was supposed to be located on the support, affecting its acidity. Rhodium interacts strongly with the support in the order: alumina> Mg–Al oxide > magnesia. The magnesium-containing catalysts showed low ethene selectivity and high hydrogen selectivity while the alumina-based ones showed high ethene selectivity, assigned to the Lewis sites of alumina. The Mg–Al oxide-supported rhodium and cobalt catalyst was the most promising sample to produce hydrogen by ethanol reforming, showing the highest hydrogen yield, low ethene selectivity and high specific surface area during reaction.     

Chiroptical effects in planar achiral plasmonic oriented nanohole arrays

Chiroptical effects are routinely observed in three dimensional objects lacking mirror symmetry or quasi-two-dimensional thin films lacking in-plane mirror symmetry. Here we show that symmetric plasmonic planar arrays of circular nanoholes produced strong chiroptical responses at visible wavelengths on tilting them with respect to the incident light beam due to the collective asymmetric nature of their surface plasmon excitations. This extrinsic chiroptical effect can be stronger than the local chiroptical response in arrays of intrinsically chiral nanoholes and may be useful for chiral sensing and negative refraction.     

Fault simulation and response compaction in full scan circuits using HOPE

This paper presents results on fault simulation and response compaction on ISCAS 89 full scan sequential benchmark circuits using HOPE-a fault simulator developed for synchronous sequential circuits that employs parallel fault simulation with heuristics to reduce simulation time in the context of designing space-efficient support hardware for built-in self-testing of very large-scale integrated circuits. The techniques realized in this paper take advantage of the basic ideas of sequence characterization previously developed and utilized by the authors for response data compaction in the case of ISCAS 85 combinational benchmark circuits, using simulation programs ATALANTA, FSIM, and COMPACTEST, under conditions of both stochastic independence and dependence of single and double line errors in the selection of specific gates for merger of a pair of output bit streams from a circuit under test (CUT). These concepts are then applied to designing efficient space compression networks in the case of full scan sequential benchmark circuits using the fault simulator HOPE.     

ModelTalk: When Everything Is a Domain-Specific Language

Many see a great future for domain-specific software development. Yet, the path to fulfilling the potential of domain-specific languages on a large scale remains largely uncharted. This article presents ModelTalk, a model-driven framework for DSL-based development. ModelTalk can be used to produce a product line of commercial business support systems for the telecommunications industry.     

A Local Facility Location Algorithm for Large-scale Distributed Systems

In a facility location problem (FLP) we are given a set of facilities and a set of clients, each of which is to be served by one facility. The goal is to decide which subset of facilities to open, such that the clients will be served at a minimal cost. In this paper we investigate the FLP in a setting where the cost depends on data known only to the clients. This setting typifies modern distributed systems: peer-to-peer file sharing networks, Grid systems, and wireless sensor networks. All of them need to perform network organization, data placement, collective power management, and other tasks of this kind. We propose a local and efficient algorithm that solves FLP in these settings. The algorithm presented here is extremely scalable, entirely decentralized, requires no routing capabilities, and is resilient to failures and changes in the data throughout its execution.