Publications

<i>Hospital Bureaucracy: A Comparative Study of Organizations.</i>Wolf V. Heydebrand

Error Performance of Chaotic Digital Code-Divison Multiple Access (CDMA) Systems

Chaotic digital code-division multiple access ((CD) 2 MA) systems are new types of communication systems using chaotic carriers. (CD) 2 MA had found applications in both wireless and other communication systems. In this paper we study the error performance of chaotic digical code-division multiple access ((CD) 2 MA) systems used in both wireless environment and cable networks. We present first the details of the interleave mode of the (CD) 2 MA. When a (CD) 2 MA system works in the interleave mode, each of its transmitters only transmits signals during a portion of the bit duration of the message signal. The total interference level is thus reduced which in turn increases the channel capacity. The relationship between the bit error rate (BER) and the interleave rate is studied in both the synchronous (CD) 2 MA system used in cable systems, and the asynchronous (CD) 2 MA system used in wireless environments. Our simulation results show that in a cable system the synchronous (CD) 2 MA system can support 1.5 times more channel capacity than synchronous CDMA systems, and double the channel capacity of CDMA systems in wireless environments.

Nano-fabricated plasmonic optical transformer

The present invention provides a plasmonic optical transformer to produce a highly focuses optical beam spot, where the transformer includes a first metal layer, a dielectric layer formed on the first metal layer, and a second metal layer formed on the dielectric layer, where the first metal layer, the dielectric layer, and the second layer are patterned to a shape including a first section having a first cross section, a second section following the first section having a cross-section tapering from the first section to a smaller cross-section, and a third section following the second section having a cross-section matching the tapered smaller cross-section of the second section.

A combinatorial approach to synthetic transcription factor‐promoter combinations for yeast strain engineering

Abstract Despite the need for inducible promoters in strain development efforts, the majority of engineering in Saccharomyces cerevisiae continues to rely on a few constitutively active or inducible promoters. Building on advances that use the modular nature of both transcription factors and promoter regions, we have built a library of hybrid promoters that are regulated by a synthetic transcription factor. The hybrid promoters consist of native S. cerevisiae promoters, in which the operator regions have been replaced with sequences that are recognized by the bacterial LexA DNA binding protein. Correspondingly, the synthetic transcription factor (TF) consists of the DNA binding domain of the LexA protein, fused with the human estrogen binding domain and the viral activator domain, VP16. The resulting system with a bacterial DNA binding domain avoids the transcription of native S. cerevisiae genes, and the hybrid promoters can be induced using estradiol, a compound with no detectable impact on S. cerevisiae physiology. Using combinations of one, two or three operator sequence repeats and a set of native S. cerevisiae promoters, we obtained a series of hybrid promoters that can be induced to different levels, using the same synthetic TF and a given estradiol. This set of promoters, in combination with our synthetic TF, has the potential to regulate numerous genes or pathways simultaneously, to multiple desired levels, in a single strain.

CCDC 879065: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Tantalum-Mediated Substitution at Germanium:  A Germolyl-to-Germole Transformation Leading to η⁴-C₄Me₄GeMeCl Complexes

The germole reagent C4Me4GeMeSiMe3 (1), synthesized via reaction of K[C4Me4GeSiMe3] with MeI, reacted with TaCl5 to give [(η4-C4Me4GeMeCl)TaCl3(Et2O)x]2 (2; x = 0.5−1.0) with loss of Me3SiCl. Complex 2 reacted with various two-electron donors to give stable adducts (η4-C4Me4GeMeCl)TaCl3L (3, L = PPh3; 4, L = CNXyl; Xyl = 2,6-dimethylphenyl) and (η4-C4Me4GeMeCl)TaCl3L2 (5, L = CNXyl; 6, L = pyridine). The X-ray structure of (η4-C4Me4GeMeCl)TaCl3(CNXyl)2 (5) confirmed η4-coordination of the germole unit and the exo orientation of the Ge−Cl bond. Complex 2 also reacted with CpTl to give air-stable Cp(η4-C4Me4GeMeCl)TaCl2 (7), which was also characterized by X-ray crystallography. Attempts to generate η5-germolyl tantalum complexes are described.

Hoplite: Efficient Collective Communication for Task-Based Distributed Systems.

Collective communication systems such as MPI offer high performance group communication primitives at the cost of application flexibility. Today, an increasing number of distributed applications (e.g, reinforcement learning) require flexibility in expressing dynamic and asynchronous communication patterns. To accommodate these applications, task-based distributed computing frameworks (e.g., Ray, Dask, Hydro) have become popular as they allow applications to dynamically specify communication by invoking tasks, or functions, at runtime. This design makes efficient collective communication challenging because (1) the group of communicating processes is chosen at runtime, and (2) processes may not all be ready at the same time. We design and implement Hoplite, a communication layer for task-based distributed systems that achieves high performance collective communication without compromising application flexibility. The key idea of Hoplite is to use distributed protocols to compute a data transfer schedule on the fly. This enables the same optimizations used in traditional collective communication, but for applications that specify the communication incrementally. We show that Hoplite can achieve similar performance compared with a traditional collective communication library, MPICH. We port a popular distributed computing framework, Ray, on atop of Hoplite. We show that Hoplite can speed up asynchronous parameter server and distributed reinforcement learning workloads that are difficult to execute efficiently with traditional collective communication by up to 8.1x and 3.9x, respectively.

CCDC 2175412: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

GRB 080319C: KAIT OA candidate.

The relationship between acute stress disorder and posttraumatic stress disorder: A prospective evaluation of motor vehicle accident survivors.

Image Processing in Tunneling Phase Logic Cellular Nonlinear Networks

Book Review:Hospital Organization Research: Review and Source Book. Basil S. Georgopoulos

The Role of Surface Roughening in Improving the Selectivity of Copper for CO₂ Electroreduction

Electroreduction of CO 2 (eCO 2 RR) has emerged as a promising alternative for production of renewable fuels and important commodity chemicals such as ethylene and ethanol. Simultaneously, it opens an economically attractive path to mitigate point sources of CO 2 , a potent greenhouse gas. Despite decades of research efforts, Cu remains the only catalyst capable of producing significant amounts of desirable C 2+ products, containing more than one carbon atom. However, further improvement is needed for industrial applications. It is known that roughened copper-based electrocatalysts surfaces exhibit enhanced selectivity towards C 2+ products during electroreduction of CO 2 . This poses a challenge for modeling efforts aiming to find a rationale for the enhanced selectivity. In this work, we use an innovative modeling approach to investigate roughened copper surfaces derived from cuprous oxide on structures of 100x100 nm 2 size with atomic resolution and accuracy compared to density functional theory (DFT). We combine semilocal DFT (RPBE) in VASP, effective medium theory (EMT), and linear scaling relationships via the recently proposed alpha parameter scheme to investigate the site-resolved catalytic selectivity of copper sites. Electrode potential-dependence is included via the use of the VASPsol implicit solvation and a grand canonical potential approach. The approach allows us to investigate the effect of varied macroscopic roughness on the intrinsic catalytic activity of copper by comparing surfaces exposed to simulated sputtering and electropolishing, respectively. The study highlights i) the challenge for designing improved copper catalysts for CO 2 RR with monodisperse active site selectivity, ii) the need for careful experimentation when comparing to theory, and iii) the limitations of macroscopic roughness in controlling atomic scale activity.

Detecting Curvilinear Structure in Images

Humans have a well developed ability to detect curvilinear structure in noisy images. Good algorithms for performing this process would be very useful in machine vision for image segmentation and object recognition. Previous approaches to this problem such as those due to Parent and Zucker and Sha'shua and Ullman have been based on relaxation. We have developed a simple feedforward and parallel approach to this problem based on the idea of developing filters tuned to local oriented circular arcs. This provides a natural second order generalization of the idea of directional operators popular for edge detection. Curve detection can then be done by methods very similar to those used for edge detection. Experimental results are shown on both synthetic and natural images. We also review data from an experiment investigating human preattentive line segregation and present predictions from our model that agree with this data. (February 1991, Revised April 1991)

Brief announcement

Designing a flexible, yet secure communication infrastructure has long been an elusive goal. Most of the proposals that seek to address the problem of flexibility have opened up the system for new forms of attacks. In this paper, we consider one particular proposal, i3 [2], a flexible indirection infrastructure that provides natural support for a multitude of communication primitives such as multicast, anycast and mobility. We systematically identify the attacks on i3, and propose techniques that address the security problems without sacrificing the flexibility that i3 offers. Our techniques, ranging from cryptographically constraining the forwarding entries to challenge-based mechanisms for inserting forwarding entries, while being simple, both conceptually and to implement, make most of the attacks provably hard. We believe that this paper represents an important step towards designing communication infrastructures that are both secure and flexible.

Atomic-scale factors that control the rate capability of nanostructured\n amorphous Si for high-energy-density batteries

Nanostructured Si is the most promising high-capacity anode material to\nsubstantially increase the energy density of Li-ion batteries. Among the\nremaining challenges is its low rate capability as compared to conventional\nmaterials. To understand better what controls the diffusion of Li in the\namorphous Li-Si alloy, we use a novel machine-learning potential trained on\nmore than 40,000 ab-initio calculations and nanosecond-scale molecular dynamics\nsimulations, to visualize for the first time the delithiation of entire LiSi\nnanoparticles. Our results show that the Si host is not static but undergoes a\ndynamic rearrangement from isolated atoms, to chains, and clusters, with the Li\ndiffusion strongly governed by this Si rearrangement. We find that the Li\ndiffusivity is highest when Si segregates into clusters, so that Li diffusion\nproceeds via hopping between the Si clusters. The average size of Si clusters\nand the concentration range over which Si clustering occurs can thus function\nas design criteria for the development of rate-improved anodes based on\nmodified Si.\n

Computational Design and Preparation of Cation‐Disordered Oxides for High‐Energy‐Density Li‐Ion Batteries

Cation‐disordered lithium‐excess metal oxides have recently emerged as a promising new class of high‐energy‐density cathode materials for Li‐ion batteries, but the exploration of disordered materials has been hampered by their vast and unexplored composition space. This study proposes a practical methodology for the identification of stable cation‐disordered rocksalts. Here, it is established that the efficient method, which makes use of special quasirandom structures, correctly predicts cation‐ordering strengths in agreement with accurate Monte‐Carlo simulations and experimental observations. By applying the approach to the composition space of ternary oxides with formula unit Li A 0.5 B 0.5 O 2 ( A , B : transition metals), this study discovers a previously unknown cation‐disordered structure, LiCo 0.5 Zr 0.5 O 2 , that may function as the basis for a new class of cation‐disordered cathode materials. This computational prediction is confirmed experimentally by solid‐state synthesis and subsequent characterization by powder X‐ray diffraction demonstrating the potential of the computational screening of large composition spaces for accelerating materials discovery.

Efficient alkene hydrosilation with bis(8-quinolyl)phosphine (NPN) nickel catalysts. The dominant role of silyl-over hydrido-nickel catalytic intermediates

A cationic nickel complex of the bis(8-quinolyl)(3,5-di-<italic>tert</italic>-butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl]⁺, is a precursor to efficient catalysts for the hydrosilation of alkenes with hydrosilanes under mild conditions and low catalyst loadings.