The Ion-Dipole Effect is a Force for Molecular Recognition and Biomimetic Catalysis

Chapter 1 In aqueous and organic media, electron-rich synthetic macrocycles serve as hosts for positively-charged guests. Binding studies in different solvents have quantified hydrophobic, donor/acceptor, and ion-dipole interactions as forces for molecular recognition. We have found clear evidence for substantial host-guest donor/acceptor π-stacking interactions (ca. 1.5 kcal/mol) in aqueous media only. The ion-dipole effect is an appreciable driving force (worth up to 3.5 kcal/mol) for molecular recognition in both aqueous and organic media. Chapter 2 Variable-temperature binding studies were performed to assess enthalpic (ΔH°) and entropic (ΔS°) contributions to free energies (ΔG°) of host-guest complexation. The van't Hoff plots (RlnKₐ vs T⁻¹), which are clearly non-linear, have revealed significant values for the heat capacities (ΔCₚ) of complexation in both organic and aqueous media. The ΔCₚ values reflect a phenomenon generally overlooked in molecular recognition studies: both ΔH° and ΔS° are strongly temperature-dependent. Hydrophobic, donor/acceptor, and ion-dipole interactions are tentatively partitioned into ΔH° and ΔS° contributions at 298K. "Classic" hydrophobic binding is characterized by a large, positive ΔS° and a near-zero ΔH° term. Strong donor/acceptor π-stacking interactions are typically balanced between large, favorable enthalpic and unfavorable entropic contributions. The ion-dipole effect is primarily an enthalpically-driven binding force. Chapter 3 Electron-rich synthetic macrocyclic host 1 accelerates a class of alkylation reactions in aqueous media. Specifically, host 1 catalyzes the reactions of pyridine-type nucleophiles with alkyl halides in an aqueous pD~9 borate buffer. The rate constants of catalyzed versus uncatalyzed reactions and the binding affinities for substrates and products demand that host 1 binds transition states more tightly than ground states. This extension of molecular recognition through ion-dipole interactions to biomimetic catalysis provides compelling evidence for transition-state stabilization via favorable dipole-dipole interactions in aqueous media. Chapter 4 A new class of high-symmetry, water soluble, hydrophobic binding sites is described that feature 1,5-substituents on a rigid ethenoanthracene (DEA) framework. These new 1,5-hosts are compared to the analogous 2,6-hosts described in the Ph.D. theses of Petti and Shepodd. Because of more favorable solvation (by water) of amide linker groups that line the cavity, the 1,5-hosts exhibit significantly reduced affinities for all guests considered: only positively-charged guests are bound to any appreciable extent. While the binding sites designed herein are composed of topographically well-defined, rigid units to give a chiral host (with a "greater sense of twist"), the disposition of the 1,5-substituents allows the collapse of hosts into a "bowl" conformation. We therefore suggest that the more successful high-symmetry, hydrophobic binding sites are to be found with 2,6-DEA-constructed hosts rather than with 1,5-DEA-constructed hosts. One benefit of the synthetic approach taken here is the development of a series of DEA building blocks for the construction of hosts with even more pronounced hydrophobic character.</p

Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer

This paper characterizes three novel microwave applicators based on zero-order mode resonators for use in hyperthermia treatment of cancer. The radiation patterns are studied with numerical simulations in muscle tissue-equivalent model at 434 MHz. The relative performance of the applicators is compared in terms of reflection coefficient, current distribution, power deposition (SAR) pattern, effective field size in 2D and 3D tissue volumes, and penetration depth. One particular configuration generated the most uniform SAR pattern, with 25% SAR covering 84 % of the treatment volume extending to 1 cm depth under the aperture, while remaining above 58% coverage as deep as 3 cm under the aperture. Recommendations are made to further optimize this structure

The Rotational Evolution of Young, Binary M Dwarfs

We have analysed K2 light curves for more than 3,000 low mass stars in the $\sim$8 Myr old Upper Sco association, the $\sim$125 Myr age Pleiades open cluster and the $\sim$700 Myr old Hyades and Praesepe open clusters to determine stellar rotation rates. Many of these K2 targets show two distinct periods, and for the lowest mass stars in these clusters virtually all of these systems with two periods are photometric binaries. The most likely explanation is that we are detecting the rotation periods for both components of these binaries. We explore the evolution of the rotation rate in both components of photometric binaries relative to one another and to non-photometric binary stars. In Upper Sco and the Pleiades, these low mass binary stars have periods that are much shorter on average and much closer to each other than would be true if drawn at random from the M dwarf single stars. In Upper Sco, this difference correlates strongly with the presence or absence of infrared excesses due to primordial circumstellar disks -- the single star population includes many stars with disks, and their rotation periods are distinctively longer on average than their binary star cousins of the same mass. By Praesepe age, the significance of the difference in rotation rate between the single and binary low mass dMs is much less, suggesting that angular momentum loss from winds for fully-convective zero-age main sequence stars erases memory of the rotation rate dichotomy for binary and single very low mass stars at later ages.Comment: accepted by A

Non-Universality in Semi-Directed Barabasi-Albert Networks

In usual scale-free networks of Barabasi-Albert type, a newly added node selects randomly m neighbors from the already existing network nodes, proportionally to the number of links these had before. Then the number N(k) of nodes with k links each decays as 1/k^gamma where gamma=3 is universal, i.e. independent of m. Now we use a limited directedness in the construction of the network, as a result of which the exponent gamma decreases from 3 to 2 for increasing m.Comment: 5 pages including 2 figures and computer progra

Double-walled carbon nanotube-based polymer composites for electromagnetic protection.

In this paper, we present a microwave absorber based on carbon nanotubes (CNT) dispersed inside a BenzoCycloButenw (BCB) polymer. The high aspect ratio and remarkable conductive characteristics of CNT give rise to good absorbing properties for electromagnetic protecting in microelectronic devices with very low concentration. In this article, nanocomposites are prepared using a solution-mixing method and are then evaluated and modeled by means of coplanar test structures. First, CNT concentrations are quantified by image processing. The nanocomposites implemented with coplanar test waveguides are then characterized using a vector network analyzer from 40 MHz to 20 GHz. An algorithm is developed to calculate the propagation constant "γ" constant "α", and relative effective complex permittivity (εreff = εreff' - jεreff'') for each CNT concentration. The extracted effective parameters are verified using the electromagnetic FEM-based Ansoft’s® high frequency structure simulator (HFSS). Power absorption (PA) of 7 dB at 15 GHz is obtained with only 0.37 weight percent of CNT concentration in the polymer matrix. The resulting engineerable and controllable composite provides consequently a novel degree of freedom to design and optimize innovative microwave components

Novel Microwave Applicators Based on Zero-Order Mode Resonance for Hyperthermia Treatment of Cancer

In this paper, three novel microwave applicator prototypes based on zero-order mode resonators are proposed for use in hyperthermia treatment of cancer. The ability of all three applicators to homogenously irradiate muscle tissue-equivalent phantoms is demonstrated with results of numerical simulations, and relative performance of the applicators is compared

FDDI network test adaptor error injection circuit

An apparatus for injecting errors into a FDDI token ring network is disclosed. The error injection scheme operates by fooling a FORMAC into thinking it sent a real frame of data. This is done by using two RAM buffers. The RAM buffer normally accessed by the RBC/DPC becomes a SHADOW RAM during error injection operation. A dummy frame is loaded into the shadow RAM in order to fool the FORMAC. This data is just like the data that would be used if sending a normal frame, with the restriction that it must be shorter than the error injection data. The other buffer, the error injection RAM, contains the error injection frame. The error injection data is sent out to the media by switching a multiplexor. When the FORMAC is done transmitting the data, the multiplexor is switched back to the normal mode. Thus, the FORMAC is unaware of what happened and the token ring remains operational

Polynomial Mixing of the Edge-Flip Markov Chain for Unbiased Dyadic Tilings

We give the first polynomial upper bound on the mixing time of the edge-flip Markov chain for unbiased dyadic tilings, resolving an open problem originally posed by Janson, Randall, and Spencer in 2002. A dyadic tiling of size n is a tiling of the unit square by n non-overlapping dyadic rectangles, each of area 1/n, where a dyadic rectangle is any rectangle that can be written in the form [a2^{-s}, (a+1)2^{-s}] x [b2^{-t}, (b+1)2^{-t}] for a,b,s,t nonnegative integers. The edge-flip Markov chain selects a random edge of the tiling and replaces it with its perpendicular bisector if doing so yields a valid dyadic tiling. Specifically, we show that the relaxation time of the edge-flip Markov chain for dyadic tilings is at most O(n^{4.09}), which implies that the mixing time is at most O(n^{5.09}). We complement this by showing that the relaxation time is at least Omega(n^{1.38}), improving upon the previously best lower bound of Omega(n*log n) coming from the diameter of the chain