A fully computerized modular scanning tunneling microscope system

Summary We have developed a fully computerized scanning tunneling microscope (STM) based on an AT-compatible computer equipped with a digital-signal-processor (DSP). All functions of the instrument, such as coarse approach, feedback-control, and scan, are under complete digital control. An Inchworm is used for coarse approach and a single tube scanner for x-, y-, and z-motions. The design is modular and, thus, open to future improvements of single components and a variety of different applications.     

Production of charged kaons by e+e− collisions between √s = 3.6 and 5 GeV

The total cross section for K^± production in e⁺e^? collisions was measured for cms energies between 3.6 and 5 GeV and was found to increase by a factor of 2–3 from 3.6 to 4.1 GeV.     

An analysis of the charged and neutral energy flow in e+e− hadronic annihilation at 34 GeV,and a determination of the QCD effective coupling constant

Using both charged and neutral components, 2600 multihadronic e⁺e^? annihilation events, recorded at 34 GeV by the CELLO detector at PETRA, have been analysed in a calometric approach. The fraction of energy carried by gamma rays is measured to be f_γ = (26.0 ± 0.4 (stat) ± 4.0 (syst)%. The neutral energy flow is seen to follow closely the overall energy flow. From the corrected oblateness distribution, a first order determination of α_s is performed. The result is α_s = 0.16 ± 0.01 (stat) ± 0.03 (syst).     

Analysis of benzene, toluene, ethylbenzene, xylenes and n-aldehydes in melted snow water via solid-phase dynamic extraction combined with gas chromatography/mass spectrometry

The present study describes a method based on headspace-solid-phase dynamic extraction (HS-SPDE) followed by GC/MS for the qualitative and quantitative analysis of benzene, toluene, ethylbenzene, o-, m- and p-xylene (BTEX), and n-aldehydes (C(6)-C(10)) in water. To enhance the extraction capability of the HS-SPDE a new cooling device was tested that controls the temperature of the SPDE needle during extraction. Extraction and desorption parameters such as the number of extraction cycles, extraction temperature, desorption volume and desorption flow rate have been optimized. Detection limits for BTEX ranged from 19 ng/L (benzene) to 30 ng/L (m/p-xylene), while those for n-aldehydes ranged from 21 ng/L (n-heptanal) to 63 ng/L (n-hexanal). At a concentration level of 2 microg/L, the relative standard deviations (RSDs) for BTEX ranged from 3.9% (benzene) to 15.3% (ethylbenzene), while RSDs for n-aldehydes were between 6.1% (n-octanal) and 16.5% (n-hexanal) (n=7). Best results were obtained when the analyzed water samples were heated to 50 degrees C. At a water temperature of 70 degrees C GC responses decreased for all analyzed compounds. At a defined water temperature, a significant improvement of the GC response was achieved by cooling of the SPDE fiber during water extraction in comparison to an extraction keeping the fiber at room temperature. Evaluating the extraction cycles, for BTEX, the sensitivity was almost similar using 20, 40 and 60 extraction cycles. In contrast, the highest GC responses for n-aldehydes were achieved by the use of 60 extraction cycles. Optimizing the desorption parameters, best results were achieved using the smallest technical available desorption volume of 500 microL and the highest technical desorption flow rate of 50 microL/s. The method was applied to the analysis of melted snow samples taken from the Jungfraujoch, Switzerland (3580 m asl), revealing the presence of BTEX and aldehydes in snow.     

The transition from inertial to viscous flow in capillary rise

We investigate the initial moments of capillary rise of liquids in a tube. In this period both inertia and viscous flow losses balance the pressure generated by the meniscus curvature (capillary pressure). It is known that the very first stage is purely dominated by inertial forces, where subsequently the influence of viscosity increases (visco-inertial flow). Finally the effect of inertia vanishes and the flow becomes purely viscous. In this study we derive the times and meniscus heights at which the transition between the time periods occur. This is done in an attempt to provide a method to determine a priori which terms of the momentum balance are relevant for a given problem. Analytic solutions known from previous literature are discussed and the time intervals of their validity compared. The predicted transition times and the calculated heights show good agreement with experimental results from literature. The results are also discussed in dimensionless form and the limitations of the calculations are pointed out.     

An integrated portable hand-held analyser for real-time isothermal nucleic acid amplification

A compact hand-held heated fluorometric instrument for performing real-time isothermal nucleic acid amplification and detection is described. The optoelectronic instrument combines a Printed Circuit Board/Micro Electro Mechanical Systems (PCB/MEMS) reaction detection/chamber containing an integrated resistive heater with attached miniature LED light source and photo-detector and a disposable glass waveguide capillary to enable a mini-fluorometer. The fluorometer is fabricated and assembled in planar geometry, rolled into a tubular format and packaged with custom control electronics to form the hand-held reactor. Positive or negative results for each reaction are displayed to the user using an LED interface. Reaction data is stored in FLASH memory for retrieval via an in-built USB connection. Operating on one disposable 3 V lithium battery >12, 60 min reactions can be performed. Maximum dimensions of the system are 150 mm (h) × 48 mm (d) × 40 mm (w), the total instrument weight (with battery) is 140 g. The system produces comparable results to laboratory instrumentation when performing a real-time nucleic acid sequence-based amplification (NASBA) reaction, and also displayed comparable precision, accuracy and resolution to laboratory-based real-time nucleic acid amplification instrumentation. A good linear response (R² = 0.948) to fluorescein gradients ranging from 0.5 to 10 μM was also obtained from the instrument indicating that it may be utilized for other fluorometric assays. This instrument enables an inexpensive, compact approach to in-field genetic screening, providing results comparable to laboratory equipment with rapid user feedback as to the status of the reaction.     

Use of a variably sensitive selected reaction monitoring method to extend the linear dynamic range for quantitative high-performance liquid chromatography/tandem mass spectrometry

A method has been devised with the capacity to extend the linear dynamic range of a triple quadrupole mass spectrometer operated in the selected reaction monitoring (SRM) mode of analysis. This extended range experiment can be realized by simultaneously acquiring variably sensitive data, via collision energy adjustment, for the same precursor-to-product ion transition within a single SRM method. While this method can be applied universally to many different study types without any detrimental effect to the analysis or throughput, it was applied herein to acquire and quantify, within a single analysis, the concentrations of GSK-A in a multiple-dose rodent study, that previously required a dilution scheme. Using this methodology, the linear dynamic range of GSK-A was increased over traditional methods by nearly two orders of magnitude, from 2.00-10,000 ng/mL to 0.500-100,000 ng/mL.     

Product design based on discrete particle modeling of a fluidized bed granulator

Fluidized bed agglomeration is a process commonly used to construct powdered food or pharmaceuti cal products to improve their instant properties. This works analyzes the influence of a wide range of operating parameters （i.e., fluidization air flow rate, temperature, and liquid injection rate） on growth rate, process stability, and product particle structure. Different granulator configurations （i.e., top spray, Wurster coater, spouted bed） are compared using identical process parameters. The impacts of both pro cess variables and granulator geometry on the fluidization regime, the particle and collision dynamics, and the resulting product structure and corresponding properties are studied in detailed simulations using a discrete particle model （DPM） and labscale agglomeration experiments with amorphous dextrose syrup （DE21）. The combination of numerical and experimental results allows to correlate the kinetics of micro scale particle interactions and the final product properties （i.e., agglomerate structure and strength）. In conclusion, detailed DPM simulations are proven as a valuable tool for knowledgebased product design.