The analysis of volatile liquid mixtures by thermal conductivity measurements on their vapors

The composition of solutions of volatile liquids can be determined by volatilization into a stream of inert gas and measurement of the thermal conductivity of the resulting gas mixture. The method is directly applicable to binary liquid mixtures which do not show maxima or minima in the conductivity-composition curve and, with modification, it may be applied to the analysis of other mixtures.The observed and calculated thermal conductivities for the acetone— water— nitrogen system showed good agreement that was typical of a number of systems     

Spectra and structure of phosphorus-boron compounds : IV. Vibrational spectra of solid trifluorophosphineborane

The Raman spectra of F₃PBH₃ and F₃PBD₃ have been recorded (2500-10 cm⁻¹) of the liquids (−80°C) and solids (−196°C) as well as the infrared spectra (4000-33 cm⁻¹) of the solids. In the spectrum of the solid state many of the ¹⁰B and ¹¹B fundamentals were clearly defined and it was also possible to assign the BH₃ torsional frequency from the infrared and Raman spectra of the solids. A complete vibrational assignment is proposed and a normal coordinate calculation carried out. The force constant of 2.46 mdyn Å⁻¹ for the P-B stretching mode is consistent with the short P-B bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. All of the E modes for the “free” molecule are shown to be split by the site symmetry which indicates that the molecules occupy C_s or C₁ sites. The large number of observed lattice modes is consistent with two or more molecules per primitive cell. The torsional frequency was observed at 224 cm⁻¹ and 167 cm⁻¹ in hydrogen and deuterium compounds in the solid, respectively. These frequencies gave a periodic barrier of 4.15 kcal mole⁻¹ for F₃PBH₃ and 4.31 kcal mole⁻¹ for F₃PBD₃. CNDO/2 calculations have been carried out for F₃PBH₃ and the isoelectronic F₃SiCH₃ molecule in both the staggered and eclipsed forms and the dipole and barrier origins are discussed.     

Applying cost minimization techniques to hospitals: A comment

In a challenging paper, [Suthummanon S., Omachonu V.K., 2007. Cost minimization models: Applications in a teaching hospital. European Journal of Operational Research 186, 1175–1183] (hereafter SO), present an interesting cost minimization model to be applied to improve hospital efficiency. Though the technical aspects of the statistical analysis SO present cannot be criticized, it is argued that the application to hospital costs the authors present is fraught with conceptual and practical problems. These need to be resolved before a length of stay approach to minimizing hospital costs can have any practical relevance.     

实数系基本定理等价性的完全互证

综合给出了实数系六个基本定理的等价性的完全互证方法,并归纳了各种证明方法的规律,旨在把抽象的证明转化为容易掌握的基本方法.     

Implementation strategies of a contract-based MRI examination reservation process for stroke patients

Timely imaging examinations are critical for stroke patients due to the potential life threat. We have proposed a contract-based Magnetic Resonance Imaging (MRI) reservation process [1] in order to reduce their waiting time for MRI examinations. Contracted time slots (CTS) are especially reserved for Neural Vascular Department (NVD) treating stroke patients. Patients either wait in a CTS queue for such time slots or are directed to Regular Time Slot (RTS) reservation. This strategy creates “unlucky” patients having to wait for lengthy RTS reservation. This paper proposes and analyzes other contract implementation strategies called RTS reservation strategies. These strategies reserve RTS for NVD but do not direct patients to regular reservations. Patients all wait in the same queue and are served by either CTS or RTS on a FIFO (First In First Out) basis. We prove that RTS reservation strategies are able to reduce the unused time slots and patient waiting time. Extensive numerical results are presented to show the benefits of RTS reservation and to compare various RTS reservation strategies.     

Likelihood and sample size: The understandings of students and their teachers

The aim of this study was to consider the match of student statistical understanding and teacher pedagogical content knowledge in relation to sample size and likelihood. Students were given two contexts within which to compare the likelihood of events for different sample sizes. Teachers were presented with one of the contexts and asked what their students would do and how they would remediate incorrect responses. The data also provided the opportunity for a detailed hierarchical analysis of students’ and teachers’ understandings. Analysis of student solutions revealed a wide range of reasoning, some of which was apparently unfamiliar to teachers.     

某情形洛必达法则的相关证明

分析部分教材对极限式分母趋于无穷大情形下的洛必达法则的证明,指出相关文献给出的证明过程存在局限甚至失误,随后通过引入一个恒等式,给出关于此情形下洛必达法则的一个完整证明,此外,还运用上、下极限给出此情形下洛必达法则的一个新证明．     

Determination of fluoroquinolone antibiotics in hospital and municipal wastewaters in Coimbra by liquid chromatography with a monolithic column and fluorescence detection

The main goal of this work was determination of residues of the antibiotics ofloxacin (OFLO), norfloxacin (NOR), ciprofloxacin (CIPRO), and enrofloxacin (ENRO) in wastewater samples. The samples, after acidification to pH 4.5 and addition of EDTA, were extracted on an anion-exchange cartridge in tandem with an Oasis HLB cartridge. The LC–FD method, developed in previous studies, was based on application of a monolithic C₁₈ column. The limit of quantification (LOQ) of the method was 250 ng L⁻¹ for OFLO, 25 ng L⁻¹ for NOR and CIPRO, and 50 ng L⁻¹ for ENRO. Mean recovery ranged between 75 and 121% for OFLO, NOR, CIPRO, and ENRO. A total of 14 wastewater samples were analyzed; these were collected from four hospitals and from influent and effluent from a wastewater-treatment plant in Coimbra, Portugal, during spring and autumn. CIPRO was present in all the samples, NOR was detected second most often, followed by OFLO. ENRO was found at concentrations under the LOQ in five hospital samples, and the highest level was found in influent from the WWTP.