Contribución del tablero y de la subestructura frente al pandeo global de pilas esbeltas de hormigón armado : determinación simplificada de una "coacción equivalente"

Las pilas de los puentes son elementos habitualmente verticales que, generalmente, se encuentran sometidos a un estado de flexión compuesta. Su altura significativa en muchas ocasiones y la gran resistencia de los materiales constituyentes de estos elementos – hormigón y acero – hace que se encuentren pilas de cierta esbeltez en la que los problemas de inestabilidad asociados al cálculo en segundo orden debido a la no linealidad geométrica deben ser considerados. Además, la mayoría de las pilas de nuestros puentes y viaductos están hechas de hormigón armado por lo que se debe considerar la fisuración del hormigón en las zonas en que esté traccionado. Es decir, el estudio del pandeo de pilas esbeltas de puentes requiere también la consideración de un cálculo en segundo orden mecánico, y no solo geométrico. Por otra parte, una pila de un viaducto no es un elemento que pueda considerarse como aislado; al contrario, su conexión con el tablero hace que aparezca una interacción entre la propia pila y aquél que, en cierta medida, supone una cierta coacción al movimiento de la propia cabeza de pila. Esto hace que el estudio de la inestabilidad de una pila esbelta de un puente no puede ser resuelto con la “teoría del pandeo de la pieza aislada”. Se plantea, entonces, la cuestión de intentar definir un procedimiento que permita abordar el problema complicado del pandeo de pilas esbeltas de puentes pero empleando herramientas de cálculo no tan complejas como las que resuelven “el pandeo global de una estructura multibarra, teniendo en cuenta todas las no linealidades, incluidas las de las coacciones”. Es decir, se trata de encontrar un procedimiento, que resulta ser iterativo, que resuelva el problema planteado de forma aproximada, pero suficientemente ajustada al resultado real, pero empleando programas “convencionales” de cálculo que sean capaces de : - por una parte, en la estructura completa: o calcular en régimen elástico lineal una estructura plana o espacial multibarra compleja; - por otra, en un modelo de una sola barra aislada: o considerar las no linealidades geométricas y mecánicas a nivel tensodeformacional, o considerar la no linealidad producida por la fisuración del hormigón, o considerar una coacción “elástica” en el extremo de la pieza. El objeto de este trabajo es precisamente la definición de ese procedimiento iterativo aproximado, la justificación de su validez, mediante su aplicación a diversos casos paramétricos, y la presentación de sus condicionantes y limitaciones. Además, para conseguir estos objetivos se han elaborado unos ábacos de nueva creación que permiten estimar la reducción de rigidez que supone la fisuración del hormigón en secciones huecas monocajón de hormigón armado. También se han creado unos novedosos diagramas de interacción axil-flector válidos para este tipo de secciones en flexión biaxial. Por último, hay que reseñar que otro de los objetivos de este trabajo – que, además, le da título - era cuantificar el valor de la coacción que existe en la cabeza de una pila debido a que el tablero transmite las cargas de una pila al resto de los integrantes de la subestructura y ésta, por tanto, colabora a reducir los movimientos de la cabeza de pila en cuestión. Es decir, la cabeza de una pila no está exenta lo cual mejora su comportamiento frente al pandeo. El régimen de trabajo de esta coacción es claramente no lineal, ya que la rigidez de las pilas depende de su grado de fisuración. Además, también influye cómo las afecta la no linealidad geométrica que, para la misma carga, aumenta la flexión de segundo orden de cada pila. En este documento se define cuánto vale esta coacción, cómo hay que calcularla y se comprueba su ajuste a los resultados obtenidos en el l modelo no lineal completo. The piers of the bridges are vertical elements where axial loads and bending moments are to be considered. They are often high and also the strength of the materials they are made of (concrete and steel) is also high. This means that slender piers are very common and, so, the instabilities produced by the second order effects due to the geometrical non linear effects are to be considered. In addition to this, the piers are usually made of reinforced concrete and, so, the effects of the cracking of the concrete should also be evaluated. That is, the analysis of the instabilities of te piers of a bridge should consider both the mechanical and the geometrical non linearities. Additionally, the pier of a bridge is not a single element, but just the opposite; the connection of the pier to the deck of the bridge means that the movements of the top of the pier are reduced compared to the situation of having a free end at the top of the pier. The connection between the pier and the deck is the reason why the instability of the pier cannot be analysed using “the buckling of a compressed single element method”. So, the question of defining an approximate method for analysing the buckling of the slender piers of a bridge but using a software less complex than what it is needed for analysing the “ global buckling of a multibeam structure considering all t”, is arisen. Then, the goal should be trying to find a procedure for analysing the said complex problem of the buckling of the slender piers of a bridge using a simplified method. This method could be an iterative (step by step) procedure, being accurate enough, using “normal” software having the following capabilities: - Related to the calculation of the global structure o Ability for calculating a multibesam strucutre using elastic analysis. - Related to the calculation of a single beam strcuture:: o Ability for taking into account the geometrical and mechanical () non linearities o Ability for taking into account the cracking of the concrete. o Ability for using partial stiff constraints (elastic springs) at the end of the elements One of the objectives of this document is just defining this simplified methodology, justifying the accuracy of the proposed procedure by using it on some different bridges and presenting the exclusions and limitations of the propose method. In addition to this, some new charts have been created for calculating the reduction of the stiffness of hollow cross sections made of reinforced concrete. Also, new charts for calculating the reinforcing of hollow cross sections under biaxial bending moments are also included in the document. Finally, it is to be said that another aim of the document – as it is stated on the title on the document – is defining the value of the constraint on the top of the pier because of the connection of the pier to the deck .. and to the other piers. That is, the top of the pier is not a free end of a beam and so the buckling resistance of the pier is significantly improved. This constraint is a non-elastic constraint because the stiffness of each pier depends on the level of cracking. Additionally, the geometrical non linearity is to be considered as there is an amplification of the bending moments due to the increasing of the movements of the top of the pier. This document is defining how this constraints is to be calculated; also the accuracy of the calculations is evaluated comparing the final results with the results of the complete non linear calculations

Aberrant protective force generation during neural provocation testing and the effect of treatment in patients with neurogenic cervicobrachial pain

Background: Observation of the occurrence of protective muscle activity is advocated in assessment of the peripheral nervous system by means of neural provocation tests. However, no studies have yet demonstrated abnormal force generation in a patient population. Objectives: To analyze whether aberrations in shoulder girdle-elevation force during neural tissue provocation testing for the median nerve (NTPTI) can be demonstrated, and whether possible aberrations can be normalized following cervical mobilization. Study Design: A single-blind randomized comparative controlled study. Setting: Laboratory setting annex in a manual therapy teaching practice. Participants: Twenty patients with unilateral or bilateral neurogenic cervicobrachial pain. Methods: During the NTPTI, we used a load cell and electrogoniometer to record continuously the shoulder-girdle elevation force in relation to the available range of elbow extension. Following randomization, we analyzed the immediate treatment effects of a cervical contralateral lateral glide mobilization technique (experimental group) and therapeutic ultrasound (control group). Results: On the involved side, the shoulder-girdle elevation force occur-red earlier, and the amount of force at the end of the test was substantially, though not significantly, greater than that on the uninvolved side at the corresponding range of motion. Together with a significant reduction in pain perception after cervical mobilization, a clear tendency toward normalization of the force curve could be observed, namely, a significant decrease in force generation and a delayed onset. The control group demonstrated no differences. Conclusions: Aberrations in force generation during neural, provocation testing are present in patients with neurogenic pain and can be normalized with appropriate treatment modalities.

Growing semiconductor nanocrystals directly in a conducting polymer

We describe a single step method to synthesise lead sulphide (PbS) nanocrystals directly in the conjugated polymer poly (2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV). This method allows size control of the nanocrystal via co-solvent ratios. We find good agreement between nanocrystal sizes determined by transmission electron microscopy and sizes theoretically determined from the absorption edge of the nanocrystals. Finally we show that this synthesis technique is not restricted to MEH-PPV and demonstrate that nanocrystals can be grown in Poly(3-hexylthiophene-2,5-diyl) (P3HT). (C) 2005 Elsevier B.V. All rights reserved.

Acupressure for the in-patient treatment of nausea and vomiting in early pregnancy: A randomized control trial

Objective: The purpose of this study was to evaluate the efficacy of acupressure at the P6 point for the in-patient treatment of severe nausea and vomiting in early pregnancy. Study design: This was a prospective single-blind randomized control trial that involved 80 patients with nausea and vomiting plus ketonuria before 14 weeks of gestation. Results: There was no difference between length of stay, amount of medication, or fluid required between the acupressure and placebo groups, although acupressure reduced the number of patients who stayed >= 4 nights in the hospital. Acupressure was well tolerated and not associated with an increase in perinatal morbidity or death. Conclusion: The use of acupressure Lit the P6 point does not reduce the amount of antiemetric medication that is required, the requirement for intravenous fluid, and median duration of inpatient stay more than the use of placebo. A small reduction was seen in the number of women who required >= 4 days in the hospital. (c) 2006 Mosby, Inc. All rights reserved.

Efficacy of speech pathology management for chronic cough: a randomised placebo controlled trial of treatment efficacy

Background: Chronic cough that persists despite medical treatment may respond to speech pathology intervention, but the efficacy of such treatment has not been investigated in prospective randomised trials. The aim of this study was to determine the efficacy of a speech pathology intervention programme for chronic cough. Methods: A single blind, randomised, placebo controlled trial was conducted in 87 patients with chronic cough that persisted despite medical treatment. Patients were randomly allocated to receive either a specifically designed speech pathology intervention or a placebo intervention. Participants in both groups attended four intervention sessions with a qualified speech pathologist. Results: Participants in the treatment group had a significant reduction in cough (8.9 to 4.6, p, 0.001), breathing (7.9 to 4.7, p < 0.001), voice (7.3 to 4.6, p < 0.001) upper airway (8.9 to 5.9, p < 0.001) symptom scores and limitation (2.3 to 1.6, p < 0.001) ratings following intervention. There was also a significant reduction in breathing (6.8 to 5.6, p=0.047), cough (7.6 to 6.3, p=0.014), and limitation ( 2.3 to 2.0, p=0.038) scores in the placebo group, but the degree of improvement was significantly less than in the treatment group (p < 0.01). Clinical judgement of outcome indicated successful ratings in 88% of participants in the treatment group compared with 14% in the placebo group ( p, 0.001). Conclusion: Speech pathology is an effective management intervention for chronic cough which may be a viable alternative for patients who do not respond to medical treatment.

Progressive resistance training and stretching following surgery for breast cancer: study protocol for a randomised controlled trial

Background: Currently 1 in 11 women over the age of 60 in Australia are diagnosed with breast cancer. Following treatment, most breast cancer patients are left with shoulder and arm impairments which can impact significantly on quality of life and interfere substantially with activities of daily living. The primary aim of the proposed study is to determine whether upper limb impairments can be prevented by undertaking an exercise program of prolonged stretching and resistance training, commencing soon after surgery. Methods/design: We will recruit 180 women who have had surgery for early stage breast cancer to a multicenter single-blind randomized controlled trial. At 4 weeks post surgery, women will be randomly assigned to either an exercise group or a usual care ( control) group. Women allocated to the exercise group will perform exercises daily, and will be supervised once a week for 8 weeks. At the end of the 8 weeks, women will be given a home-based training program to continue indefinitely. Women in the usual care group will receive the same care as is now typically provided, i.e. a visit by the physiotherapist and occupational therapist while an inpatient, and receipt of pamphlets. All subjects will be assessed at baseline, 8 weeks, and 6 months later. The primary measure is arm symptoms, derived from a breast cancer specific questionnaire (BR23). In addition, range of motion, strength, swelling, pain and quality of life will be assessed. Discussion: This study will determine whether exercise commencing soon after surgery can prevent secondary problems associated with treatment of breast cancer, and will thus provide the basis for successful rehabilitation and reduction in ongoing problems and health care use. Additionally, it will identify whether strengthening exercises reduce the incidence of arm swelling. Trial Registration: The protocol for this study is registered with the Australian Clinical Trials Registry (ACTRN012606000050550).

Generation of primary hepatocyte microarrays by piezoelectric printing

We demonstrate a single-step method for the generation of collagen and poly-l-Lysine (PLL) micropatterns on a poly(ethylene glycol) (PEG) functionalized glass surface for cell based assays. The method involves establishing a reliable silanization method to create an effective non-adhesive PEG layer on glass that inhibits cell attachment, followed by the spotting of collagen or PLL solutions using non-contact piezoelectric printing. We show for the first time that the spotted protein micropatterns remain stable on the PEG surface even after extensive washing, thus significantly simplifying protein pattern formation. We found that adherence and spreading of NIH-3T3 fibroblasts was confined to PLL and collagen areas of the micropatterns. In contrast, primary rat hepatocytes adhered and spread only on collagen micropatterns, where they formed uniform, well defined functionally active cell arrays. The differing affinity of hepatocytes and NIH-3T3 fibroblasts for collagen and PLL patterns was used to develop a simple technique for creating a co-culture of the two cell types. This has the potential to form structured arrays that mimic the in vivo hepatic environment and is easily integrated within a miniaturized analytical platform for developing high throughput toxicity analysis in vitro.

Developing solid particulate vaccine adjuvants - surface bound antigen favouring a humoural response, whereas entrapped antigen shows a tendency for cell mediated immunity

This present study compares the efficacy of microsphere formulations, and their method of antigen presentation, for the delivery of the TB sub-unit vaccine antigen, Ag85B-ESAT-6. Microspheres based on poly(lactide-co-glycolide) (PLGA) and chitosan incorporating dimethyldioctadecylammonium bromide (DDA) were prepared by either the w/o/w double emulsion method (entrapped antigen) or the o/w single emulsion method (surface bound antigen), and characterised for their physico-chemical properties and their ability to promote an immune response to Ag85B-ESAT-6. The method of preparation, and hence method of antigen association, had a pronounced effect on the type of immune response achieved from the microsphere formulations, with surface bound antigen favouring a humoural response, whereas entrapped antigen favoured a cellular response.

Developing solid particulate vaccine adjuvants:surface bound antigen favouring a humoural response, whereas entrapped antigen shows a tendency for cell mediated immunity

This present study compares the efficacy of microsphere formulations, and their method of antigen presentation, for the delivery of the TB sub-unit vaccine antigen, Ag85B-ESAT-6. Microspheres based on poly(lactide-co-glycolide) (PLGA) and chitosan incorporating dimethyldioctadecylammonium bromide (DDA) were prepared by either the w/o/w double emulsion method (entrapped antigen) or the o/w single emulsion method (surface bound antigen), and characterised for their physico-chemical properties and their ability to promote an immune response to Ag85B-ESAT-6. The method of preparation, and hence method of antigen association, had a pronounced effect on the type of immune response achieved from the microsphere formulations, with surface bound antigen favouring a humoural response, whereas entrapped antigen favoured a cellular response.

Acute mobile phone operation affects neural function in humans

OBJECTIVES: Mobile phones (MP) are used extensively and yet little is known about the effects they may have on human physiology. There have been conflicting reports regarding the relation between MP use and the electroencephalogram (EEG). The present study suggests that this conflict may be due to methodological differences such as exposure durations, and tests whether exposure to an active MP affects EEG as a function of time. METHODS: Twenty-four subjects participated in a single-blind fully counterbalanced cross-over design, where both resting EEG and phase-locked neural responses to auditory stimuli were measured while a MP was either operating or turned off. RESULTS: MP exposure altered resting EEG, decreasing 1-4 Hz activity (right hemisphere sites), and increasing 8-12 Hz activity as a function of exposure duration (midline posterior sites). MP exposure also altered early phase-locked neural responses, attenuating the normal response decrement over time in the 4-8 Hz band, decreasing the response in the 1230 Hz band globally and as a function of time, and increasing midline frontal and lateral posterior responses in the 30-45 Hz band. CONCLUSIONS: Active MPs affect neural function in humans and do so as a function of exposure duration. The temporal nature of this effect may contribute to the lack of consistent results reported in the literature.

Can the Q Link Ally,® a form of sympathetic resonance technology (SRT™), sttenuate scute mobile phone-related changes to neural function?

OBJECTIVES: Exposure to active mobile phones (MP) has been shown to affect human neural function as shown by the electroencephalogram (EEG). Although it has not been determined whether such effects are harmful, a number of devices have been developed that attempt to minimize these MP-related effects. One such device, the Q Link Ally® (QL; Clarus Products, International, L.L.C., San Rafael, CA), is argued to affect the human organism in such a way as to attenuate the effect of MPs. The present pilot study was designed to determine whether there is any indication that QL does alter MP-related effects on the human EEG. DESIGN: Twenty-four (24) subjects participated in a single-blind, fully counterbalanced crossover design in which subjects' resting EEG and phase-locked neural responses to auditory stimuli were assessed under conditions of either active MP or active MP plus QL. RESULTS: The addition of QL to the MP condition increased resting EEG in the gamma range and did so as a function of exposure duration, and it attenuated MP-related effects in the delta and alpha range (at trend-level). The addition of the QL also affected phase-locked neural responses, with a laterality reversal in the alpha range and an alteration to changes over time in the delta range, a reduction of the MP-related beta decrease over time at fronto-posterior sites, and a global reduction in the gamma range that increased as a function of exposure duration. No unambiguous relations were found between these changes and either performance or psychologic state. CONCLUSIONS: This pilot study suggests that the addition of the QL to active MP-exposure does affect neural function in humans, altering both resting EEG patterns and the evoked neural response to auditory stimuli, and that there is a tendency for some MP-related changes to the EEG to be attenuated by the QL.

Immunological synapse: a mathematical model of the bond formation process:mathematical modelling of the immature synapse

The cell:cell bond between an immune cell and an antigen presenting cell is a necessary event in the activation of the adaptive immune response. At the juncture between the cells, cell surface molecules on the opposing cells form non-covalent bonds and a distinct patterning is observed that is termed the immunological synapse. An important binding molecule in the synapse is the T-cell receptor (TCR), that is responsible for antigen recognition through its binding with a major-histocompatibility complex with bound peptide (pMHC). This bond leads to intracellular signalling events that culminate in the activation of the T-cell, and ultimately leads to the expression of the immune eector function. The temporal analysis of the TCR bonds during the formation of the immunological synapse presents a problem to biologists, due to the spatio-temporal scales (nanometers and picoseconds) that compare with experimental uncertainty limits. In this study, a linear stochastic model, derived from a nonlinear model of the synapse, is used to analyse the temporal dynamics of the bond attachments for the TCR. Mathematical analysis and numerical methods are employed to analyse the qualitative dynamics of the nonequilibrium membrane dynamics, with the specic aim of calculating the average persistence time for the TCR:pMHC bond. A single-threshold method, that has been previously used to successfully calculate the TCR:pMHC contact path sizes in the synapse, is applied to produce results for the average contact times of the TCR:pMHC bonds. This method is extended through the development of a two-threshold method, that produces results suggesting the average time persistence for the TCR:pMHC bond is in the order of 2-4 seconds, values that agree with experimental evidence for TCR signalling. The study reveals two distinct scaling regimes in the time persistent survival probability density prole of these bonds, one dominated by thermal uctuations and the other associated with the TCR signalling. Analysis of the thermal fluctuation regime reveals a minimal contribution to the average time persistence calculation, that has an important biological implication when comparing the probabilistic models to experimental evidence. In cases where only a few statistics can be gathered from experimental conditions, the results are unlikely to match the probabilistic predictions. The results also identify a rescaling relationship between the thermal noise and the bond length, suggesting a recalibration of the experimental conditions, to adhere to this scaling relationship, will enable biologists to identify the start of the signalling regime for previously unobserved receptor:ligand bonds. Also, the regime associated with TCR signalling exhibits a universal decay rate for the persistence probability, that is independent of the bond length.