一种用于地面和有线接收机的宽带低噪声放大器

提出并设计了一种用于数字电视接收调谐芯片的宽带低噪声放大器.该设计采用0.35μm SiGe BiCMOS工艺,器件的主要性能为:增益等于18.8dB,增益平坦度小于1.4dB,噪声系数小于5dB,1dB压缩点为-2dBm,输入三阶交调为8dBm.在5V供电的情况下,直流功耗为120mW.     

Turbidity dynamics during spring storm events in an urban headwater river system: the Upper Tame, West Midlands, UK

Turbidity is an important water quality variable, through its relation to light suppression, BOD impact, sediment-associated contaminant transport, and suspended sediment effects on organisms and habitats. Yet few published field investigations of wet-weather turbidity dynamics, through several individual and sequenced rainstorms in extremely urbanised headwater basins, have emerged. This paper aims to address this gap through a turbidity analysis of multiple storm events in spring 2001 in an urban headwater basin (57 km2) of the River Tame, central England, the most urbanised basin for its size in the UK ( approximately 42%). Data were collected at 15-min frequency at automated monitoring stations for rainfall, streamflow and six water quality variables (turbidity, EC, temperature, DO, pH, ammonia). Disturbance experiments also allowed estimates of bed sediment storage to be obtained. Six important and unusual features of the storm event turbidity response were apparent: (1) sluggish early turbidity response, followed by a turbidity 'rush'; (2) quasi-coincident flow and turbidity peaks; (3) anti-clockwise hysteresis in the discharge-turbidity relationship on all but one event, resulting from Falling-LImb Turbidity Extensions (FLITEs); (4) increases in peak turbidity levels through storm sequences; (5) initial micro-pulses (IMP) in turbidity; and (6) secondary turbidity peaks (STP) or 'turbidity shoulders' (TS). These features provided very little evidence of a true 'first-flush' effect: instead, substantial suspended solids transport continued right through the flow recessions, and little storm-event sediment exhaustion was evident. A new, dimensionless, hysteresis index, HI(mid), is developed to quantify the magnitude and direction of hysteresis in a simple, clear, direct and intuitive manner. This allowed the degree of departure from the classic 'first-flush', clockwise hysteresis models to be assessed. Of the 15 turbidity events considered, 10 coincided with ammonia spikes of up to 6.25 mg l(-1) at Water Orton (the downstream station): this suggests that spills from combined sewer overflows (CSO) or waste water treatment works (WwTWs) are significant in the throughput of turbid waters here. Substantial ammonia peaks related most strongly to total storm rainfall receipt, of four rainfall variables considered, and significant ammonia peaks were generated even from low-magnitude storms (rainfall totals <4 mm), indicating that spills are a frequent occurrence. Local bed sediment stores appear to be limited, suggesting that other distal sediment sources, such as road networks and old mineworkings are possibly more important. Biofilms may also play a part in delaying sediment release until late in the hydrograph, and in suppressing late spring turbidity levels. Existing first-flush models appear to be an oversimplification here. Such urban headwater basin responses can provide useful insights into the generation of contaminant waves, and offer vital early-warning systems for pollution events propagating downstream.     

Comparison of oral,intravenous, and subcutaneous fluid therapy for resuscitation of calves with diarrhea

Neonatal diarrhea remains the primary cause of mortality in dairy calves around the world, and optimal treatment protocols are needed. The main goals of therapy are to restore hydration and electrolyte concentrations, correct strong ion (metabolic) acidemia, and provide nutritional support. Administration of oral electrolyte solutions (OES) has long been the primary method used to treat neonatal diarrhea in humans and calves because OES are capable of addressing each of the primary goals of therapy. In calves with moderate dehydration, we hypothesized that oral electrolytes would be as good as or better than small volumes of intravenous (IV) or subcutaneous (SC) fluids. Therefore, the main goal of this study was to compare the ability of a commercially available oral electrolyte solution (OES) administered alone or in combination with hypertonic saline with small volumes of IV or SC fluid therapy to resuscitate calves with diarrhea. Thirty-three Holstein calves from 5 to 14 d of age were utilized in this clinical trial. Diarrhea and dehydration were induced by adding sucrose to the milk replacer. In addition, hydrochlorothiazide and spironolactone were given orally and furosemide intramuscularly. Depression status, clinical hydration scores, fecal consistency, and body weight were recorded at regular intervals. Treatment began when calves had severe diarrhea and had a decrease in plasma volume of at least 10%. Calves were randomly assigned to 1 of 4 treatment groups of 8 to 9 calves per group: (1) OES; (2) OES with hypertonic saline (4 mL/kg, IV); (3) IV fluids (lactated Ringer's, 2 L); or (4) SC fluids (lactated Ringer's, 2 L). Treatments were given at 0 and 12 h. Changes in plasma volume, blood pH, electrolyte levels, and physical examination scores were determined before therapy and again at 1, 2, 4, 8, and 12 h after each treatment. All 4 treatments were ultimately successful in improving hydration as well as increasing blood pH; however, animals in both groups that received OES had much faster resuscitation than those in either the IV or SC fluid group. In conclusion, oral electrolyte products remain the gold standard for resuscitating diarrheic calves with moderate dehydration and acidemia and will likely perform better than small volumes of IV lactated Ringer's solution. Subcutaneous fluids by themselves are a poor treatment option and should be only be used as supportive therapy following the initial correction of hypovolemia and metabolic acidosis.     

Professor Geoffrey Petts (1953–2018): An outstanding interdisciplinary river scientist

This paper provides an introduction and an editorial to this special issue of River Research and Applications by documenting the contributions made by Professor Geoffrey Petts to our interdisciplinary understanding of the functioning of rivers and their floodplains and their sustainable management. We outline Geoff's career, which framed not only his research but its communication through his inspirational teaching but also included very high level and innovative contributions to the management and development of several UK universities. We then explain how and why Geoff was an outstanding interdisciplinary river scientist and how he communicated his science through both integrative books and book chapters and also research papers that developed eight complementary research themes. Lastly, we introduce the papers in this special issue and show how they provide inputs to Geoff's areas of research interest.     

Rheology of starch dispersions at high temperatures

In the food industry, many food products experience extreme processing conditions of high temperature and high shear stresses. The measurements of sample behavior for water-based formulations above 100°C is extremely challenging due to changes in material composition from the boiling of volatile ingredients. We have developed a high-sensitivity, pressurized starch pasting cell (up to 5 bar) which utilizes a design free of mechanical bearings and seals, resulting in an order-of-magnitude improvement in torque sensitivity (1 μN.m in oscillatory and 10 μN.m in shear flows) compared to traditional pressure cells. A pressurized atmosphere in the cell suppresses boiling of the volatile components, allowing the characterization of the structure–property relationships of the sample over a range of testing conditions (−5 to 150°C) which simulate industrial processing and storage conditions. This cell is employed to investigate the pasting properties of a commercial starch dispersed in water. In situ gelatinization of starch dispersions of varying starch particle weight fractions (ϕ) subjected to a high temperature (120°C) at elevated pressure and at a fixed shear rate is studied. A phase transition, from an initial flowable starch slurry to a paste, takes place during which the viscosity evolves by several orders of magnitude. Typical parameters associated with the viscosity evolution during gelatinization such as onset temperature, peak temperature, and peak viscosity are analyzed to probe the impact of high temperature on the gelation process and the rheological properties of the final starch paste. Furthermore, yield stresses of the final paste, measured at 120°C, are examined for varying ϕ through traditional rheological methods such as flow ramps, oscillatory shear, and stress growth, demonstrating the capabilities of this cell for studies of steady shear and nonlinear viscoelastic behavior of the starch pastes. The yield stress values are found to be in good agreement when comparing various testing methods. Yield stresses range from 0.25 to 6.5 Pa for ϕ between 0.05 and 0.15, with 0.05 being the minimum starch weight fraction for which there is any measurable yield stress. The yield stress and the paste viscosity both scale with starch particle weight fraction as (ϕ − ϕ_c) ^m, where ϕ_c = 0.04 as no yield stress is observed for ϕ ≤ 0.04. The exponent, m, for yield stress is found to be in the range of 1.15–1.4 depending on the analytical method used and the definition of yield stress while for peak and breakdown viscosities it is noted to be 1.6 and 1.1, respectively. The Herschel-Bulkley model is found to fit the flow curves well. The starch pastes are found to exhibit shear-thinning and significant thixotropic behavior.     

Effects of plasma treatment on biocompatibility of poly[(L‐lactide)‐co‐(ϵ‐caprolactone)] and poly[(L‐lactide)‐co‐glycolide] electrospun nanofibrous membranes

Poly[(l ‐lactide)‐co ‐(? ‐caprolactone)] (PLCL) and poly[(l ‐lactide)‐co ‐glycolide] (PLGA) copolymers are widely used in neural guide tissue regeneration. In this research, the surface modification of their hydrophilicity was achieved using plasma treatment. Attachment and proliferation of olfactory ensheathing cells on treated electrospun membranes increased by 26 and 32%, respectively, compared to the untreated PLCL and PLGA counterparts. Cells cultivated on both the PLCL and PLGA membranes showed high viability (>95%) and healthy morphologies with no evidence of cytotoxic effects. Cells grown on treated electrospun fibres displayed significant increases in mitochondrial activity and reductions in membrane leakage when compared to untreated samples. The results suggested that plasma treatment of the surface of the polymers enhanced both cell viability and growth without incurring any cytotoxic effects. © 2017 Society of Chemical Industry