Electrochemical oxidation analysis for dressing bronze-bonded diamond grinding wheels

Electrochemical dressing of fine-grained metal-bonded diamond grinding wheels enables to grind hard and brittle materials in the ductile mode. Optical surfaces can be manufactured by grinding, which reduces the need for subsequent, time-consuming polishing work. When using metal-bonded grinding wheels, the emerging oxides regulate the electrochemical dissolution. Bronze-bonded grinding wheels are more suitable for grinding cemented carbides and ceramics than iron-bonded grinding wheels, as it is easier to modify their chemical composition to suit a specific grinding task. They can also be sintered at lower temperatures, which reduces the risk of thermal damage to the diamond. In this paper, the dissolution and the oxidation of different bronze alloys are characterized for the electrochemical dressing process. The relevant evaluation criteria are the oxide layer thickness, the electrical behavior and the different emerging bronze alloy oxides. This work is funded by the German Research Association DFG within the Transregional Collaborative Research Center SFB/TR4 “Process Chains for the Replication of Complex Optical Elements”.     

“From microtiter plates to droplets” tools for micro-fluidic droplet processing

Droplet-based microfluidic allows high throughput experimentation in with low volume droplets. Essential fluidic process steps are on the one hand the proper control of the droplet composition and on the other hand the droplet processing, manipulation and storage. Beside integrated fluidic chips, standard PTFE-tubings and fluid connectors can be used in combination with appropriate pumps to realize almost all necessary fluidic processes. The segmented flow technique usually operates with droplets of about 100–500 nL volume. These droplets are embedded in an immiscible fluid and confined by channel walls. For the integration of segmented flow applications in established research workflows—which are usually base on microtiter plates—robotic interface tools for parallel/serial and serial/parallel transfer operations are necessary. Especially dose–response experiments are well suited for the segmented flow technique. We developed different transfer tools including an automated “gradient take-up tool” for the generation of segment sequences with gradually changing composition of the individual droplets. The general working principles are introduced and the fluidic characterizations are given. As exemplary application for a dose–response experiment the inhibitory effect of antibiotic tetracycline on Escherichia coli bacteria cultivated inside nanoliter droplets was investigated.     

A study of 3D cover glass design that improves handheld device drop reliability

Cover glass in commercial handheld devices is now evolving from flat (2D) to curved (3D) shapes. For example, some commercial devices have utilized sled‐shape cover glass, 1 which partially covers long edges of the device. According to the patents published by key handheld manufacturers, 2 , 3 we can expect more variety of 3D shaped cover glass for handheld devices in the market. In this study, we have focused on the reliability of 3D cover glass when it is dropped to a rigid surface. The key parameters under study are the corner/edge bend radius and angle of the cover glass, which determines the 3D shape of the cover glass. To achieve this goal, we developed a finite element model to simulate the drop 4 - 13 of a handheld device with 3D‐shaped glass. The model uses explicit algorithm to simulate the high speed impact on the device during the drop test. The glass performance was evaluated based on contact force between the glass and the ground and maximum principal stress in the glass. We showed that to avoid severe damage because of first impact between the glass and the ground, the bend angle of 3D glass has to be in the range between 0 and 45°. For drop angles of 45° and higher, with the proposed glass bend angle, the impact can be taken over by the edge of the back cover of the device. In addition, we showed that optimum glass bend radius is in the range of 3.8 mm and larger. This is required to reduce stress in glass because of impact. The approach and conclusions from the current study can serve as a general guideline to improve the 3D cover glass reliability of a handheld device.     

Path partitions of hypercubes

A path partition of a graph G is a set of vertex-disjoint paths that cover all vertices of G. Given a set of pairs of distinct vertices of the n-dimensional hypercube Qn, is there a path partition of Qn such that ai and bi are endvertices of Pi? Caha and Koubek showed that for 6m?n, such a path partition exists if and only if the set P is balanced in the sense that it contains the same number of vertices from both classes of bipartition of Qn.In this paper we show that this result holds even for 2m−e<n, where e is the number of pairs of P that form edges of Qn. Moreover, our bound is optimal in the sense that for every n?3, there is a balanced set P in Qn such that 2m−e=n, but no path partition with endvertices prescribed by P exists.     

The Effect of Target Vector Selection on the Invariance of Classifier Performance Measures

In this paper, the multiclass supervised training problem is considered when a discrete set of classes is assumed. Upon generating affine models for finite data sets, we have observed the invariance of certain measures of performance after a trained classifier has been presented with test data of unknown classification. Specifically, after constructing mappings between training vectors and their desired targets, the class membership and ranking of test data has been found to remain either invariant or close to invariant under a transformation of the set of target vectors. Therefore, we derive conditions explaining how this type of invariance can arise when the multiclass problem is phrased in the context of linear networks. A bioinformatics example is then presented in order to demonstrate various principles outlined in this work.     

Detection of low levels of trichloroethylene vapor with Raman spectrometry

The response of a novel fiber-optic Raman probe to low levels of trichloroethylene (TCE) vapors is characterized. The detection limit of the current probe for TCE vapor is 34 mg/L, and the probe exhibits a fully reversible response. The probe uses an organic-polymer, low-density polyethylene to concentrate TCE vapors in the optical path of the fiber-optic Raman spectrometer. The relative standard deviation for measurement of 677 mg/L of TCE in the vapor is 0.3%.     

Characterization of laser hardened steels by laser induced ultrasonic surface waves

Ultrasonic surface waves are suitable for the characterization of surface hardened materials. This is shown on laser hardened turbine blades. The martensitic microstructure within the surface layer of surface hardened steels has a lower surface wave propagation velocity than the annealed or normalized substrate material. Because the propagation velocity depends on the ratio of layer thickness to wavelengthd/, its measurement allows the determination of the hardening depth. If the surface wave frequency is high enough, the surface wave propagates mainly within the hardened layer. A correlation of the surface wave velocity to the surface hardness has been found. Because the variation of the surface velocity in hardened steels is small, a high measurement accuracy is necessary to obtain the interesting hardening parameters with sufficient certainty. Therefore, a measuring arrangement has been developed where laser pulses, guided by optical fibers to the surface hardened structure, generate simultaneously surface wave pulses at two different positions. The two ultrasonic pulses are received by a piezoelectric transducer. The surface wave velocity is obtained from the time delay between these pulses which is determined by the cross-correlation method. To evaluate simultaneously surface waves with different penetration depths from the same signal acquisition, digital filtering has been used in connection with the cross-correlation.     

New aspects of transversal1H-NMR relaxation in natural rubber vulcanizates

Summary Structure and dynamics of unfilled and carbon black filled natural rubber vulcanizates were investigated by means of transversal¹H-NMR-relaxation. A simple theoretical model including different motions in polymer network was extended by the discussion of an anisotropy parameter of segmental motion not only for the intercrosslink chains but also for the dangling ends. It makes characterization of the filling state of the network possible to approximate. The effect of increasing correlation times _f of the fast anisotropic local motion with reduction of the molecular mass of intercrosslink chains which was observed, but not cleared up in previous investigation is evidently smaller by using this modified model in accordance with the expectation of a local motion. The determined values of M_c are in good agreement with the results of fits by using the unmodified relaxation function.¹³C-NMR-spectra and stress-strain-experiments are leading in most cases to similar results, especially for M_c.