Protecting local access telecommunications networks: Toward a minimum-cost solution

The problem of designing fibre-optic networks for local-access telecommunications generates (at least) three non-trivial subproblems. In the first of these subproblems one must determine how many fibre-optic cables (fibres) are required at either end of a street. In the next subproblem a minimum-cost network must be designed to support the fibres. The network must also provide distinct paths from either end of the street to the central exchange(s). Finally, the fibre-optic cables must be placed in protective covers. These covers are available in a number of different sizes, allowing some flexibility when covering each section of the network. In this paper we describe a dynamic programming (DP) formulation for finding a minimum-cost (protective) covering for the network (the third of the subproblems). This problem is a generalised set covering problem with side constraints and is further complicated by the introduction of fixed and variable welding costs. The DP formulation selects covers along each arc (in the network), but cannot exactly model the fixed costs and so does not guarantee optimality. We also describe an integer programming (IP) formulation for assessing the quality of the DP solutions. The cost of the networks constructed by the IP model is less than those designed using the DP model, but the saving is not significant for the problems examined (less than 0.1%). This indicates that the DP model will generally give very good solutions. Furthermore, as the problem dimensions grow, DP gives significantly better solution times than IP.     

Life is pleasant--and memory helps to keep it that way!

People's recollections of the past are often positively biased. This bias has 2 causes. The 1st cause lies in people's perceptions of events. The authors review the results of several studies and present several new comparative analyses of these studies, all of which indicate that people perceive events in their lives to more often be pleasant than unpleasant. A 2nd cause is the fading affect bias: The affect associated with unpleasant events fades faster than the affect associated with pleasant events. The authors review the results of several studies documenting this bias and present evidence indicating that dysphoria (mild depression) disrupts such bias. Taken together, this evidence suggests that autobiographical memory represents an important exception to the theoretical claim that bad is stronger than good. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Large deflection dynamics and control for planar continuum robots

This paper focuses on a class of robot manipulators termed "continuum" robots - robots that exhibit behavior similar to tentacles, trunks, and snakes. In previous work, we studied details of the mechanical design, kinematics, path-planning and small-deflection dynamics for continuum robots such as the Clemson "tentacle manipulator". In this paper, we discuss the dynamics of a planar continuum backbone section, incorporating a large-deflection dynamic model. Based on these dynamics, we formulate a vibration-damping setpoint controller, and include experimental results to illustrate the efficacy of the proposed controller.     

Stability of motor-unit force thresholds in the decerebrate cat

To further test the hypothesis that some fixed property of motoneurons determines their recruitment order, we quantified the variation in force threshold (FT) for motoneurons recruited in muscle stretch reflexes in the decerebrate cat. Motor axons supplying the medial gastrocnemius (MG) muscle were penetrated with micropipettes and physiological properties of the motoneuron and its muscle fibers, i.e., the motor unit, were measured. FT, defined as the amount of MG force produced when the isolated motor unit was recruited, was measured from 20 to 93 consecutive stretch trials for 29 motor units. Trials were selected for limited variation in base force and rate of rise of force, which have been shown to covary with FT, and in peak stretch force, which gives some index of motor-pool excitability. Under these restricted conditions, large variation in FT would have been inconsistent with the hypothesis. Analysis of the variation in FT employed the coefficient of variation (CV), because of the tendency for FT variance and mean to increase together. We found that CV was distributed with a median value of 10% and with only 2 of 29 units exceeding 36%. Some of this variation was associated with measurement error and with intertrial fluctuations in base, peak, and the rate of change of muscle force. CV was not significantly correlated with motor-unit axonal conduction velocity, contraction time, or force. In three cases FT was measured simultaneously from two motor units in the same stretch trials. Changes in recruitment order were rarely observed (5 of 121 stretch trials), even when FT ranges for units in a pair overlapped. We suggest that the large variation in recruitment threshold observed in some earlier studies resulted not from wide variation in the recruitment ranking of motoneurons within one muscle, but rather from variation in the relative activity of different pools of motoneurons. Our findings are consistent with the hypothesis that recruitment order is determined by some fixed property of alpha-motoneurons and/or by some unvarying combination of presynaptic inputs that fluctuate in parallel.     

Complications of chronic otitis media

In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications.     

The ultrasound appearances of neonatal renal vein thrombosis

Renal vein thrombosis (RVT) is the most frequently occurring vascular condition in the new-born kidney. The predisposing factors include dehydration, sepsis, birth asphyxia, maternal diabetes, polycythaemia and the presence of an indwelling umbilical venous catheter. (RVT) may present clinically with a flank mass, haematuria, hypertension or renal failure. Many imaging modalities have been employed, but ultrasound is the technique most commonly used in the evaluation of neonates with suspected RVT. Thrombosis commences in the small renal veins and subsequently propagates via larger interlobar veins to the main renal vein and inferior vena cava (IVC). The ultrasound appearances depend upon the stage at which the examination is performed and extent of the thrombus. Initially, the interlobular and interlobar thrombus appears as highly echogenic streaks. These streaks commence in a peripheral, focal segment of the involved kidney and only persist for a few days. In the first week the affected kidney swells and becomes echogenic with prominent echopoor medullary pyramids. Later, the swelling increases and the kidney becomes heterogenous with loss of corticomedullary differentiation. Grey scale ultrasound readily demonstrates thrombus within the renal vein and IVC. Adrenal haemorrhage is a recognized association and may be identified ultrasonically. Colour Doppler scanning provides additional information. In the early stages of RVT, colour Doppler may demonstrate absent intrarenal and renal venous flow. Ultimately, the kidney may recover, show focal scarring or become atrophic. Thus, ultrasound provides an accessible and reliable tool in the assessment of suspected neonatal RVT.     

Immunohistochemical localization of p21(WAF1/CIP1) in normal, hyperplastic, and neoplastic uterine tissues

Assuming that the chemical reactions used to synthesize a combinatorial library member are successful, then knowledge of the specific reaction sequence is equivalent to knowing the member's chemical identity. Because the determination of chemical identity is typically not automatable and requires a substantial amount of material, schemes that encode a member's reaction history onto the reaction platform are of value. The primary benefits of encoding are relational nomenclature (all methods) and automated handling (some methods). Encoding methods evaluated to date are spatial, graphical, chemical, spectrometric, electronic, and physical.     

Cloning and disruption of the antigenic catalase gene of Aspergillus fumigatus

Aspergillus fumigatus possesses two catalases (described as fast and slow on the basis of their electrophoretic mobility). The slow catalase has been recognized as a diagnostic antigen for aspergillosis in immunocompetent patients. The antigenic catalase has been purified. The enzyme is a tetrameric protein composed of 90-kDa subunits. The corresponding cat1 gene was cloned, and sequencing data show that the cat1 gene codes for a 728-amino-acid polypeptide. A recombinant protein expressed in Pichia pastoris is enzymatically active and has biochemical and antigenic properties that are similar to those of the wild-type catalase. Molecular experiments reveal that CAT1 contains a signal peptide and a propeptide of 15 and 12 amino acid residues, respectively. cat1-disrupted mutants that were unable to produce the slow catalase were as sensitive to H2O2 and polymorphonuclear cells as the wild-type strain. In addition, there was no difference in pathogenicity between the cat1 mutant and its parental cat1+ strain in a murine model of aspergillosis.