Theoretical and Experimental Analysis of a Vibration Isolation System Using Hybrid Magnet

AbstractAn active vibration isolation system using hybrid magnet is investigated theoretically and experimentally. A quarter car model with one degree of freedom spring mass system is considered for this analysis. A cylindrical type hybrid magnet, considered as actuator is placed in parallel to the springs to provide external force on the top and bottom plates to suppress vibration. The theoretical time response characteristics of the model have been determined and correlated with experimental analysis. For theoretical analysis, the response of the top plate is analyzed by considering the base plate disturbance as a input signal to vary the actuator force .The force exerted by the hybrid magnet is non linear in nature and the simplified relation for this force was obtained using Bessel's recurrence formula. The modeling of undamped one degree of freedom quarter car model is carried out using MATLAB Simulink tool. The above study is also investigated experimentally by employing a shaker and analyzed using LABVIEW and fast Fourier transform (FFT) analyzer

Ising pyrochlore magnets: Low temperature properties, ice rules and beyond

Pyrochlore magnets are candidates for spin-ice behavior. We present theoretical simulations of relevance for the pyrochlore family R2Ti2O7 (R= rare earth) supported by magnetothermal measurements on selected systems. By considering long ranged dipole-dipole as well as short-ranged superexchange interactions we get three distinct behaviours: (i) an ordered doubly degenerate state, (ii) a highly disordered state with a broad transition to paramagnetism, (iii) a partially ordered state with a sharp transition to paramagnetism. Thus these competing interactions can induce behaviour very different from conventional ``spin ice''. Closely corresponding behaviour is seen in the real compounds---in particular Ho2Ti2O7 corresponds to case (iii) which has not been discussed before, rather than (ii) as suggested earlier.Comment: 5 pages revtex, 4 figures; some revisions, additional data, additional co-authors and a changed title. Basic ideas of paper remain the same but those who downloaded the original version are requested to get this more complete versio

Influence of magnetic field strength of hybrid magnet on vibration isolation of quarter car model

This work studies the vibration isolation of a single degree of freedom (SDOF) quarter car model under the influence of the magnetic field strength of electromagnet of a hybrid electromagnet (EM) and permanent magnet (PM) combination. Furthermore, the time history plot helps to study the influence of the relative movement of the electromagnet and the permanent magnet on the top plate, base plate, stiffness of the system and damping coefficient. A laboratory scale model of a SDOF quarter car with a hybrid magnet is tested on an open loop type shaker table at different frequencies of base excitation. Data acquisition and analysis have been carried out with the aid of two piezoelectric accelerometers and Lab VIEW software. Also, the theoretical analysis is carried out in MATLAB Simulink. From the experimental and Simulink results, it is found that the repulsive force between the electromagnet and permanent magnet varies the base and top plate amplitude, the stiffness of the system and damping coefficient of the suspension elements

Spirograph based electrospinning system for producing fibre mat with near uniform mechanical property

This study focuses on the development of Spirograph-based mechanical system (SBMS) for the collection ofpolyacrylonitrile fibres in an electrospinning process. The collector plate is set to trace a spiropath in such a way that theevent of crossing the centre of collection region from different radial direction is high. To assess the capability of SBMS,electrospun mat of acrylic has been prepared and the properties of samples sectioned from different angular positions of acircular mat are evaluated. The diameter and alignment of fibres are analyzed by processing the scanning electronmicroscopy (SEM) images of electrospun mats with the use of ImageJ software. The electrospun mat produced using SBMScollector assembly exhibits near uniform characteristics like thickness, tensile strength, porosity, fibre diameter and fibrealignment as compared to the electrospun mat produced by using conventional static collector

Exact ground state and kink-like excitations of a two dimensional Heisenberg antiferromagnet

A rare example of a two dimensional Heisenberg model with an exact dimerized ground state is presented. This model, which can be regarded as a variation on the kagome lattice, has several features of interest: it has a highly (but not macroscopically) degenerate ground state; it is closely related to spin chains studied by earlier authors; in particular, it is probably the first genuinely two-dimensional quantum system to exhibit domain-wall-like ``kink'' excitations normally found only in one-dimensional systems. In some limits it decouples into non-interacting chains, purely dynamically and not because of weakening of interchain couplings: indeed, paradoxically, this happens in the limit of strong coupling of the chains.Comment: 4 pages, revtex, 5 figures included via epsfi

Prevalence of chronic respiratory disease in urban and rural Uganda.

OBJECTIVE: To determine the prevalence of chronic respiratory diseases in urban and rural Uganda and to identify risk factors for these diseases. METHODS: The population-based, cross-sectional study included adults aged 35 years or older. All participants were evaluated by spirometry according to standard guidelines and completed questionnaires on respiratory symptoms, functional status and demographic characteristics. The presence of four chronic respiratory conditions was monitored: chronic obstructive pulmonary disease (COPD), asthma, chronic bronchitis and a restrictive spirometry pattern. FINDINGS: In total, 1502 participants (average age: 46.9 years) had acceptable, reproducible spirometry results: 837 (56%) in rural Nakaseke and 665 (44%) in urban Kampala. Overall, 46.5% (698/1502) were male. The age-adjusted prevalence of any chronic respiratory condition was 20.2%. The age-adjusted prevalence of COPD was significantly greater in rural than urban participants (6.1 versus 1.5%, respectively; P?<?0.001), whereas asthma was significantly more prevalent in urban participants: 9.7% versus 4.4% in rural participants (P?<?0.001). The age-adjusted prevalence of chronic bronchitis was similar in rural and urban participants (3.5 versus 2.2%, respectively; P?=?0.62), as was that of a restrictive spirometry pattern (10.9 versus 9.4%; P?=?0.82). For COPD, the population attributable risk was 51.5% for rural residence, 19.5% for tobacco smoking, 16.0% for a body mass index <?18.5 kg/m2 and 13.0% for a history of treatment for pulmonary tuberculosis. CONCLUSION: The prevalence of chronic respiratory disease was high in both rural and urban Uganda. Place of residence was the most important risk factor for COPD and asthma

Systematic review of prediction models in relapsing remitting multiple sclerosis

The natural history of relapsing remitting multiple sclerosis (RRMS) is variable and prediction of individual prognosis challenging. The inability to reliably predict prognosis at diagnosis has important implications for informed decision making especially in relation to disease modifying therapies. We conducted a systematic review in order to collate, describe and assess the methodological quality of published prediction models in RRMS. We searched Medline, Embase and Web of Science. Two reviewers independently screened abstracts and full text for eligibility and assessed risk of bias. Studies reporting development or validation of prediction models for RRMS in adults were included. Data collection was guided by the checklist for critical appraisal and data extraction for systematic reviews (CHARMS) and applicability and methodological quality assessment by the prediction model risk of bias assessment tool (PROBAST). 30 studies were included in the review. Applicability was assessed as high risk of concern in 27 studies. Risk of bias was assessed as high for all studies. The single most frequently included predictor was baseline EDSS (n = 11). T2 Lesion volume or number and brain atrophy were each retained in seven studies. Five studies included external validation and none included impact analysis. Although a number of prediction models for RRMS have been reported, most are at high risk of bias and lack external validation and impact analysis, restricting their application to routine clinical practice

Functional properties of in vitro excitatory cortical neurons derived from human pluripotent stem cells

The in vitro derivation of regionally defined human neuron types from patient‐derived stem cells is now established as a resource to investigate human development and disease. Characterization of such neurons initially focused on the expression of developmentally regulated transcription factors and neural markers, in conjunction with the development of protocols to direct and chart the fate of differentiated neurons. However, crucial to the understanding and exploitation of this technology is to determine the degree to which neurons recapitulate the key functional features exhibited by their native counterparts, essential for determining their usefulness in modelling human physiology and disease in vitro. Here, we review the emerging data concerning functional properties of human pluripotent stem cell‐derived excitatory cortical neurons, in the context of both maturation and regional specificity. [Image: see text