Characterizing homogeneous chemistry using well-mixed microeddies

Well-mixed reaction volumes are often sought in engineered microchemical devices and can be an important feature of naturally occurring physicochemical processes such as pitting corrosion. Steady streaming eddies can serve as well-mixed, easily controlled microliter chemical reactors for characterizing homogeneous chemical reactions. Here, steady streaming eddies are produced by oscillating a liquid-filled cuvette around a stationary cylindrical electrode (radius 406 microm, length 1.6 cm) at audible frequencies (75 Hz). Oxidant (ferricyanide) electrochemically dosed at small rates (相似文献   

Hydrodynamic tweezers: 1. Noncontact trapping of single cells using steady streaming microeddies

A key need for dynamic single-cell measurements is the ability to gently position cells for repeated measurements without perturbing their behavior. We describe a new method that uses a gentle secondary flow to trap and suspend single cells, including motile cells, at predictable locations in 3-D. Trapped cells can be more dense or less dense than the surrounding medium. The cells are suspended without surface contact in one of four steady streaming eddies created by audible-frequency fluid oscillation (< or =1000 Hz) in a microchannel containing a single fixed cylinder (radius = 125 microm). Comparison of measured trap locations to computations of the eddy flow show that each trap is located near the eddy center, and the location is controlled via the oscillation frequency. We use the motile phytoplankton cell (Prorocentrum micans) to experimentally measure the trapping force, which is controlled via the oscillation amplitude. Trapping forces up to 30 pN are generated while exerting moderate shear stresses (shear stresses < or = 1.5 N/m2) on the trapped cell. The magnitude of this trapping force is comparable to that of optical tweezers or dielectrophoretic traps, without requiring an external field outside the physiological range for cells (the shear stresses are comparable to those found in arterial blood flow). The unique combination of predictable 3-D positioning, insensitivity to cell and medium properties, strong adjustable trapping forces, and a gentle fluid environment makes hydrodynamic tweezers a promising new option for noncontact trapping of single cells in suspension.     

Flux and product distribution during biological treatment of tetrachloroethene dense non-aqueous-phase liquid

Flux in non-aqueous-phase liquid (NAPL)-contaminated systems containing active microbial populations (including Dehalococcoides sp.) was investigated using a quantitative mass balance and phase distribution approach. Batch systems containing mixed NAPL with an initial tetrachloroethene (PCE) mole fraction ranging from 0.1 to 0.4 provided a means for comparing systems where mass transfer and aqueous concentration were controlled by the initial NAPL composition. Although the use of mixed NAPL with increasing PCE mole fractions introduced a mass-transfer variable on the abiotic dissolution rate, it was determined that biological systems produced flux rates that were similar to each other regardless of the initial PCE mole fraction. Thus, organisms appeared to be dechlorinating near their maximum conversion rates, and the result was the accumulation of cis-1,2-dichloroethene (cDCE) followed by slow conversion to vinyl chloride (VC). Increases in the initial PCE mole fractions in the NAPL had a negative impact on product distribution due to the presence of a larger concentration of a more favorable electron acceptor. Because the mass converted to cDCE was present largely in the dissolved phase in all systems, the production of this metabolite was a favorable outcome in terms of NAPL dissolution. The pH dropped as low as 4.9 in active systems, indicating that the amount of HCl released during the reductive dechlorination process was large enough to overwhelm the buffering capacity. This pH effect was more pronounced in systems that exhibited extensive dechlorination to VC, further suggesting that rapid dechlorination of PCE NAPL can alter chemical characteristics in source zone regions.     

Analysis of broadly tunable coupled-cavity semiconductor lasers

We report on the spectral properties for above-threshold operation of broadly tunable, asymmetric multiple quantum well (AMQW), coupled-cavity InGaAsP/InP semiconductor diode lasers. We developed a traveling wave model to understand the mode selection that the lasers exhibit. We find that a weak, short external cavity (SXC) can be used to obtain single frequency operation on each longitudinal mode over the ～100 nm tuning range of the uncoated AMQW coupled-cavity lasers. We measured the spectral properties of AMQW coupled-cavity lasers with and without an SXC. In a synthesized optical coherent optical tomography application, the use of an SXC with an AMQW coupled-cavity laser reduces the coherence length and hence enhances the performance of the AMQW coupled-cavity laser for optical coherence tomography applications.     

Hyperspectral Imager for the Coastal Ocean: instrument description and first images

The Hyperspectral Imager for the Coastal Ocean (HICO) is the first spaceborne hyperspectral sensor designed specifically for the coastal ocean and estuarial, riverine, or other shallow-water areas. The HICO generates hyperspectral images, primarily over the 400-900 nm spectral range, with a ground sample distance of ≈90 m (at nadir) and a high signal-to-noise ratio. The HICO is now operating on the International Space Station (ISS). Its cross-track and along-track fields of view are 42 km (at nadir) and 192 km, respectively, for a total scene area of 8000 km(2). The HICO is an innovative prototype sensor that builds on extensive experience with airborne sensors and makes extensive use of commercial off-the-shelf components to build a space sensor at a small fraction of the usual cost and time. Here we describe the instrument's design and characterization and present early images from the ISS.     

基于北斗B1C信号的DPE方法定位性能分析

城市峡谷环境的高精度定位是全球卫星导航定位系统亟待解决的重要问题之一。近年来提出的直接位置估计(Direct Position Estimation, DPE)方法是基于“导航域”实现位置的最优估计，现有研究集中于全球定位系统(Global Positioning System, GPS)信号进行分析验证，缺乏新体制信号的对比和抗多径原理分析，并且计算量过大不易实现。针对以上问题，基于北斗卫星导航系统(BDS)B1C信号，设计了一种快速DPE软件接收机，并基于城市峡谷环境下的真实信号验证了BDS B1C新体制信号DPE软件接收机的实际性能。实际试验表明，相同信号相干积分长度和卫星几何精度因子情况下，DPE接收机使用二进制偏置载波调制(Binary Offset Carrier, BOC)新体制信号相较于二进制相移键控(Binary Phase Shift Keying, BPSK)信号在城市峡谷环境下定位精度具有显著提升。     

七成消费者因质量好而续费 会员制超市需稳住价格和质量

<正>2023年7月底，盒马推出“移山价”，打响会员制超市价格战第一枪。之后两个月，盒马“移山价”从北京、上海延展到全国15座城市，山姆榴莲千层也从128元降到85元，这场朴实无华的商战愈战愈凶。前段时间，“DT商业观察”发起了一次关于会员制超市的调研，共回收到1147份有效问卷。参与调研的读者中，95后、90后和85后占比超过7成，女性占比超6成，超8成人生活在一线或新一线城市。逛会员制超市的人多吗？大家更偏好哪个超市？都在买些什么？透过这次调查，我们或许可以得到答案。     

西南地区居民腌熏制品食用行为及其影响因素分析

目的 调查西南地区腌熏制品高频食用行为现状及危险因素，并提出相应的对策建议。方法 调查时间为2021年2～5月，采取方便抽样法在西南地区（云南、贵州、四川和重庆）进行线下问卷调查获取数据，收集其地理、人口社会学因素和健康知识与行为，采取无序多分类Logistic回归分析高频腌熏制品食用行为的风险因素。结果 地理因素上，云贵地区和农村高频腌熏制品食用行为风险较高，且云南的高频腌熏制品食用风险分别是参照组重庆的2.764倍和2.126倍。人口社会学因素中，高频腌熏制品食用行为一定程度上与年龄、受教育程度呈正相关，偏智力劳动是保护因素。年龄与腌制品食用行为中，60岁以上老年人风险最高，18～25岁青年仅为该群体的46.70%。健康知识与行为上，盐的知识了解程度与熏制品食用行为有统计学差异，回答全错组风险为全对组的1.372倍。而饮酒频率与腌熏制品风险基本呈正相关关系，在两组因变量中，每周饮酒3次以上人群风险最高，从不饮酒群体仅有其32.10%。结论 腌熏制品是西南地区的特色美食，地理因素、人口社会学因素以及健康知识与行为因素均与高频腌熏制品存在关联。应控制高频饮食行为带来的健康风险，应针对云...     

安全雾计算物联网的联合资源配置方法

当前雾计算物联网系统在物理通信传输过程中容易遭受窃听攻击，现有雾计算相关研究未能有效解决这一难题，为实现雾计算物联网的物理层安全（PLS）通信以此对抗多个窃听器的恶意窃听，提出一种物理层安全雾计算物联网（PSFC-IoT）系统，并分析所提系统在安全通信场景下的系统保密速率。针对网络的资源配置问题，提出一种基于量子种子优化算法（QBOA）的联合资源配置方法，并对所提方法的收敛性进行分析。仿真实验结果证明了所提模型的有效性，并揭示了各种环境参数对系统保密性能的影响。此外，仿真结果还表明，所提方法在各种通信场景下均能获得最佳的保密性能。