Asymmetric synthesis of gonytolide A: strategic use of an aryl halide blocking group for oxidative coupling

The first synthesis of the chromanone lactone dimer gonytolide A has been achieved employing vanadium(V)-mediated oxidative coupling of the monomer gonytolide C. An o-bromine blocking group strategy was employed to favor para- para coupling and to enable kinetic resolution of (±)-gonytolide C. Asymmetric conjugate reduction enabled practical kinetic resolution of a chiral, racemic precursor and the asymmetric synthesis of (+)-gonytolide A and its atropisomer.We thank the National Institutes of Health (R35 GM-118173) for research support. Work at the BU-CMD is supported by NIH R24 Grant GM-111625. We thank Prof. Scott Miller and Dr. Anthony Metrano (Yale University) for helpful discussions and preliminary experiments. We thank the Uehara Memorial Foundation for a postdoctoral fellowship to T.I., the American Cancer Society for a postdoctoral fellowship to K.D.R. (PF-16-235-01-CDD), Dr. Jeffrey Bacon (Boston University) for X-ray crystal structure analyses, and Prof. Haruhisa Kikuchi (Tohoku University) for providing a natural sample of gonytolide A. NMR (CHE-0619339) and MS (CHE-0443618) facilities at Boston University are supported by the NSF. (R35 GM-118173 - National Institutes of Health; GM-111625 - NIH; Uehara Memorial Foundation; PF-16-235-01-CDD - American Cancer Society; CHE-0619339 - NSF; CHE-0443618 - NSF

A new pricing model of China’s parallel rail lines under the diversified property rights

Purpose: The purpose of this paper is to study on the pricing of China railway company under the background of diversified property rights, especially the pricing of the parallel line system that belong to different owners. Design/methodology/approach: Through theoretical analysis of the main influential factors of railway pricing, this paper designs a basic quotation system for the parallel railway lines. Findings: The transaction price of parallel line consists of two parts, which are fixed railway network price and variable network using price. Practical implications: Through the reasonable designing of fixed network price and variable network using price, it can not only lead to high profitability and low government subsidy, but also can ensure remaining more railway network resources and fulfill the social responsibilities. Originality/value: The conclusions of this study will lay the foundation for the harmonious development of Chinese railway network under the diversified property rights.Peer Reviewe

Modeling neutral evolution using an in nite-allele Markov branching process

We consider an in nite-allele Markov branching process (IAMBP). Our main focus is the frequency spectrum of this process, i.e., the proportion of alleles having a given number of copies at a speci ed time point. We derive the variance of the frequency spectrum, which is useful for interval estimation and hypothesis testing for process parameters. In addition, for a class of special IAMBP with birth and death o spring distribution, we show that the mean of its limiting frequency spectrum has an explicit form in terms of the hypergeometric function. We also derive an asymptotic expression for convergence rate to the limit. Simulations are used to illustrate the results for the birth and death process

Information-Coupled Turbo Codes for LTE Systems

We propose a new class of information-coupled (IC) Turbo codes to improve the transport block (TB) error rate performance for long-term evolution (LTE) systems, while keeping the hybrid automatic repeat request protocol and the Turbo decoder for each code block (CB) unchanged. In the proposed codes, every two consecutive CBs in a TB are coupled together by sharing a few common information bits. We propose a feed-forward and feed-back decoding scheme and a windowed (WD) decoding scheme for decoding the whole TB by exploiting the coupled information between CBs. Both decoding schemes achieve a considerable signal-to-noise-ratio (SNR) gain compared to the LTE Turbo codes. We construct the extrinsic information transfer (EXIT) functions for the LTE Turbo codes and our proposed IC Turbo codes from the EXIT functions of underlying convolutional codes. An SNR gain upper bound of our proposed codes over the LTE Turbo codes is derived and calculated by the constructed EXIT charts. Numerical results show that the proposed codes achieve an SNR gain of 0.25 dB to 0.72 dB for various code parameters at a TB error rate level of $10^{-2}$, which complies with the derived SNR gain upper bound.Comment: 13 pages, 12 figure

Modeling Ultrafast Laser Ablation on the Glenoid Bone for the Fitting of a Prosthetic Screw

In order to fit prosthetic screws, mechanical drilling of the bone has been the norm since the development of modern surgery. However, bone reabsorption, hyperthermia and thermo necrosis could occur depending on the exposure time to the drill and elevated temperature in the surrounding bone due to friction and drill pressure. Non-contact ablation using a CO2 laser can potentially increase the accuracy of the bone drilling and reduce the amount of friction applied to the bone, thus reducing the thermal effects on the surrounding tissue. A model of laser ablation of the human glenoid bone was done on COMSOL with a governing equation of transient state heat transfer from laser to bone. This heat transfer was then correlated to bone loss. According to previous studies, bone disintegration occurs at approximately 613 Kelvin. The bone’s geometry was simplified to a 2-D axisymmetric cylinder. The two domains of the 5mm deep screw region were also 2D-axisymmetric cylinders with varying radius and depth. The phase field model was used to take into account the ablation process of bone. Because the bone essentially disintegrates into “gas-like” particles after reaching this temperature, the phase field model was used to determine the downward velocity of the “air-bone” interface. An adaptive mesh was also developed to move in conjunction with the moving interface. The laser pattern consisted of consecutive concentric cylindrical shells, with the first pulse at the center of the targeted ablated site and the following pulses were cylindrical shells of increasing area. However, because the radial scanning speed was extremely small compared to the pulse duration, concentric cylindrical shells were assumed to occur simultaneously, creating a constant area of laser ablation for each of the two screw domains. Because the CO2 laser did not have a significant penetration depth as the heat generated by the laser was absorbed mainly at the bone surface, input laser heating was modeled as constant flux. Finally, the modeling results for laser ablation were compared to factors in mechanical bone drilling. By varying the input flux of the laser within a range of 300 W/cm2 to 1200 W/cm2 and measuring the total ablation time and the total damage in the surrounding tissue, an optimal flux range between 1050 W/cm2 and 1100 W/cm2 was found to minimize the end time (approximately 0.55 seconds) and thermal damage to the surrounding bone (3.5 mm3). Compared to mechanical drilling, laser ablation with the optimized flux value was much faster than mechanical drilling which can drill at approximately 0.33 mm per second. Generally, less surgery time decreases a patient’s risk when under anesthesia. An increased amount of thermal damage may also lead to refractures, loosening of the prosthetic and permanent loss of tissue function. As laser ablation minimized both these parameters, this model demonstrates that laser ablation of bone is a viable method to consider in future surgical orthopedic work