Modeling and Simulation of Robotic Systems with Closed Kinematic Chains Using the Virtual Spring Approach

The dynamic simulation of robotic or mechanical systems with closedkinematic chains using the virtual spring approach is presented in thispaper. This approach uses virtual springs and dampers to include thekinematic constraints thereby avoiding the solution ofdifferential-algebraic equations. A special advantage of this approachis that it leads to a completely decoupled dynamic model which is idealfor real-time dynamic simulation using multi-processor computers.Examples illustrating the approach are given and include the four-barmechanism with both rigid and flexible links as well as the six-degree-of-freedom Gough–Stewart platform. Simulation results are given for these mechanisms. The results achieve a good agreement with the resultsobtained from other conventional approaches.     

A comparison of the enantioselectivities of human deoxycytidine kinase and human cytidine deaminase

The stereoselectivities of recombinant human deoxycytidine kinase (EC 2.7.1.74) (dCK) and of recombinant human cytidine deaminase (EC 3.5.4.5) (CDA) were investigated with respect to a series of cytidine analogs, most of them having the unnatural L-stereochemistry. The enantioselectivity of dCK was always low and generally favored the L-enantiomers in the case of beta-2',3'-dideoxycytidine (beta-ddC), 5-fluoro-beta-2',3'-dideoxycytidine (beta-FddC) and beta-cytidine (beta-riboC). Concerning beta-2'-deoxycytidine, dCK showed a preference for the D-enantiomer. All other examined beta-L-cytidine analogs, [1-beta-L-lyxofuranosyl cytosine (beta-L-lyxoC), l-beta-L-xylofuranosyl cytosine (beta-L-xyloC), and 5-fluoro-1-beta-L-xylofuranosyl cytosine (beta-L-Fxylo C)], were substrates of dCK regardless of the nature of the pentose. None of the studied alpha-L-anomers (alpha-L-riboC, alpha-L-araC, alpha-L-lyxoC, or alpha-L-xyloC) was a substrate of dCK. Contrasting with the relaxed enantioselectivity of dCK, CDA had a strict requirement for D-cytidine analogs since none of the already listed beta-L- or alpha-L analogs was a substrate or an inhibitor of the enzyme. The conjunction of the preceding stereochemical properties of dCK and CDA confers to L-cytidine analogs important potentialities in antiviral and anticancer therapies.     

Selective protection of toxicity of 2',3'-dideoxypyrimidine nucleoside analogs by beta-D-uridine in human granulocyte-macrophage progenitor cells

beta-D-Uridine protected human granulocyte-macrophage lineage cells in both semi-solid (granulocyte-macrophage colony-forming units, CFU-GM) and liquid cultures against the toxic effects of 3'-azido-3'-deoxythymidine (AZT), 3'-fluoro-3'-deoxythymidine (FLT) and a combination of AZT and FLT, without impairment of the activities of these respective drugs against human immunodeficiency virus (HIV) replication. In addition, beta-D-uridine also protected human CFU-GM against toxicity of the in vivo AZT metabolite, 3'-amino-3'-deoxythymidine (AMT). Beta-L-uridine and alpha-D-uridine, two stereoisomers of the natural form, and the base uracil, were unable to protect cells against either AZT or FLT toxicity, whereas beta-D-uridine-5'-bis(SATE)phosphotriester, a prodrug of beta-D-uridine-5'-monophosphate, successfully protected cells against AZT toxic effects, suggesting that beta-D-uridine needs to be metabolized to its nucleotides to exert a pharmacological effect. These data suggest in addition that AZT, FLT and AMT share a common target site(s) of toxicity involved in myelosuppression.     

On the development of the Agile Eye

The “Agile Eye” is a high-performance mechanism capable of orienting a camera within a workspace larger than that of a human eye and with velocities and accelerations larger than those of the human eye. The mechanical design, control issues, and experimental results are presented     

Sclerosing lipogranuloma in a male

INTRODUCTION: Major trauma was the only aetiologic factor found in a male patient presenting sclerosing lipogranuloma. This condition is well-known in women but is rarely described in men. CASE REPORT: A 31-year-old non-obese man with no sign of gynaecomasty presented with well-delimited plaques of pigmented and sclerosous tissue located at the pubis and both breasts as well as hard nodules of the scrotum and the penis. The lesion developed progressively after a major trauma involving the anterior aspect of the thorax and the public area. An inflammatory border persisted eight years after the initial trauma. Histological examination of a biopsy specimen showed evidence of adipocyte necrosis with lipophagia and lipogranuloma. No foreign body was found. DISCUSSION: The diagnosis of post-trauma cytosteatonecrosis was retained on the basis of the clinical history and the clinical, histological and radiographic evidence. This condition is a well-identified clinical entity which is sometimes confounded with false panniculitis resulting from self-injection of oily products. The endogenous origin of the fatty acids found within the cytosteatonecrosis tissue has recently been proven. Usual localizations are the breast in women and genital organs in men. Favouring factors in women include obesity, age, anticoagulants, frequency and intensity of trauma. The exceptional localization in our patient was strongly related to the earlier trauma.     

A low-power integrated neural interface with digital spike detection and extraction

We present the design of an integrated neural interface intended for multi-channel neural recording. The design features a mixed-signal part that handles neural signal conditioning, digitization, time-division multiplexing, and a digital module providing control, absolute threshold detection, extraction of spikes, and serial communications towards a host interface. The detection and extraction strategy preserves the entire neuronal spike waveshapes by means of synchronized internal data buffering. This bandwidth reduction scheme prompts for better waveform sorting results and improved performance in prosthetic applications. Both parts of the presented neural interface were fabricated separately in a CMOS 0.18 μm process. The whole neural interface features 16 channels for validation, but, the proposed approach is scalable to larger channel counts. The performance of the implemented neural interface was validated on testbench with synthetic neural waveforms. It features a power consumption of 138 μW per channel and a size of 2.304 mm², and achieves a bandwidth reduction factor of up to 48.     

Singularity analysis of 5-RPUR parallel mechanisms (3T2R)

Singularities of parallel mechanisms are related to the regularity of certain Jacobian matrices whose rank deficiency makes the mechanisms lose their inherent rigidity. This paper presents the results of a detailed investigation of the singular configurations of 5-degree-of-freedom parallel mechanisms performing all three translations and two independent rotations. The general architecture of the mechanism—arising from the type synthesis of symmetrical 5-degree-of-freedom parallel mechanisms—is comprised of a mobile platform attached to a base through five identical revolute–prismatic–universal revolute-jointed serial kinematic chains. From the results of screw theory, it is demonstrated that the Jacobian matrix of the above mechanism is constituted by six Plücker lines, a special case of Grassmann coordinates. This channels us to use the so-called Grassmann line geometry instead of applying a classical linear algebra approach. Grassmann line geometry can be regarded as a classification of the degeneration of the Plücker line set. Moreover, six simplified designs are proposed for which their singular configurations can be predicted by means of the Grassmann line geometry. The principles of this study can also be applied to other types of symmetrical 5-degree-of-freedom parallel mechanisms.     

Evolutionary Placement of Discrete Heaters in Forced Convection

This article aims to maximize the global conductance (C) of a symmetrical, discretely heated channel in forced convection, where the fluid flow is sustained by a fixed pressure difference given by the Bejan number. The maximization of C is obtained by determining the optimal arrangement of the discrete heaters along the channel and the optimal channel breadth with the help of a genetic algorithm (GA) that is fully coupled with the finite-element methods used for solving the conservation equations. The number of independent variables considered in the optimization process varies between N + 1 and 2N + 1, where N is the number of heat sources (1 ≤ N ≤ 20) and the extra unit represents the channel height. The numerical results agree with the available literature, showing that increased values of C are obtained with designs that do not use equally spaced heaters. The results show that a larger number of discrete heaters can provide higher values of global conductance when compared with fully optimized simpler designs (i.e., a small number of discrete heaters), which is also in agreement with previous studies. Designs with heaters of variable heat strength are also considered, to study the optimal allocation of the total heat input through the N heaters. This family of designs leads to even higher performance.