608 research outputs found
Effect of Sensory Feedback from the Proximal Upper Limb on Voluntary Isometric Finger Flexion and Extension in Hemiparetic Stroke Subjects
This study investigated the potential influence of proximal sensory feedback on voluntary distal motor activity in the paretic upper limb of hemiparetic stroke survivors and the potential effect of voluntary distal motor activity on proximal muscle activity. Ten stroke subjects and 10 neurologically intact control subjects performed maximum voluntary isometric flexion and extension, respectively, at the metacarpophalangeal (MCP) joints of the fingers in two static arm postures and under three conditions of electrical stimulation of the arm. The tasks were quantified in terms of maximum MCP torque [MCP flexion (MCPflex) or MCP extension (MCPext)] and activity of targeted (flexor digitorum superficialis or extensor digitorum communis) and nontargeted upper limb muscles. From a previous study on the MCP stretch reflex poststroke, we expected stroke subjects to exhibit a modulation of voluntary MCP torque production by arm posture and electrical stimulation and increased nontargeted muscle activity. Posture 1 (flexed elbow, neutral shoulder) led to greater MCPflex in stroke subjects than posture 2 (extended elbow, flexed shoulder). Electrical stimulation did not influence MCPflex or MCPext in either subject group. In stroke subjects, posture 1 led to greater nontargeted upper limb flexor activity during MCPflex and to greater elbow flexor and extensor activity during MCPext. Stroke subjects exhibited greater elbow flexor activity during MCPflex and greater elbow flexor and extensor activity during MCPext than control subjects. The results suggest that static arm posture can modulate voluntary distal motor activity and accompanying muscle activity in the paretic upper limb poststroke
Modulation of Stretch Reflexes of the Finger Flexors by Sensory Feedback from the Proximal Upper Limb Poststroke
Neural coupling of proximal and distal upper limb segments may have functional implications in the recovery of hemiparesis after stroke. The goal of the present study was to investigate whether the stretch reflex response magnitude of spastic finger flexor muscles poststroke is influenced by sensory input from the shoulder and the elbow and whether reflex coupling of muscles throughout the upper limb is altered in spastic stroke survivors. Through imposed extension of the metacarpophalangeal (MCP) joints, stretch of the relaxed finger flexors of the four fingers was imposed in 10 relaxed stroke subjects under different conditions of proximal sensory input, namely static arm posture (3 different shoulder/elbow postures) and electrical stimulation (surface stimulation of biceps brachii or triceps brachii, or none). Fast (300°/s) imposed stretch elicited stretch reflex flexion torque at the MCP joints and reflex electromyographic (EMG) activity in flexor digitorum superficialis. Both measures were greatest in an arm posture of 90° of elbow flexion and neutral shoulder position. Biceps stimulation resulted in greater MCP stretch reflex flexion torque. Fast imposed stretch also elicited reflex EMG activity in nonstretched heteronymous upper limb muscles, both proximal and distal. These results suggest that in the spastic hemiparetic upper limb poststroke, sensorimotor coupling of proximal and distal upper limb segments is involved in both the increased stretch reflex response of the finger flexors and an increased reflex coupling of heteronymous muscles. Both phenomena may be mediated through changes poststroke in the spinal reflex circuits and/or in the descending influence of supraspinal pathways
Desarrollo de un guante ortótico para proveer asistencia en la extensión de los dedos a pacientes que han sufrido derrame cerebral
An externally actuated glove, controlled by a microprocessor, is being developed to assist fi nger extension in
stroke survivors. The goal of this device is to allow repeated practice of specifi c tasks for hand therapy in the home environment.
The device allows the user three control modes: voice recognition, electromyography or manual. These modes can be used either
independently or combined according to the needs of the user. Both position and force feedback are available for control and safety.
Initial testing of the prototype has shown promising performance.Se presenta el desarrollo de un guante activado externamente y controlado por un microprocesador para asistir la
extensión de los dedos en pacientes con derrame cerebral. La meta del dispositivo es permitir la repetición de tareas específi cas
para realizar terapia de la mano en un ambiente casero. El usuario puede controlar el dispositivo por tres medios diferentes:
reconocimiento de voz, electromiografía o manualmente. Estos medios pueden ser usados tanto independientemente como en
combinación según las necesidades del paciente. Para el control y la seguridad, se tiene retroalimentación de posición y de fuerza.
Las pruebas iniciales del prototipo han demostrado un desempeño prometedo
Superconduction thin films
Superconduction thin films, and properties and applications of Josephson effect at radio frequencie
Are the orthostatic fluid shifts to the calves augmented in autonomic failure?
In autonomic failure (AF), blood pressure (BP) falls upon standing which is commonly ascribed to defective vasoconstriction and excessive pooling. Observations on the amount of pooling in AF are contradictory. We evaluated pooling using strain-gauge plethysmography (SGP) during head-up tilt (HUT) with a parachute harness fixed to the tilt table to avoid muscle tension in the lower limbs and thus to maximise pooling. 23 healthy subjects and 12 patients with AF were tilted for 5 min. BP and calf volume changes, as measured by SGP, were measured continuously. Multiple regression analysis was used to examine the effect of AF on orthostatic fluid shifts after adjustment for potential confounders. Patients did not differ from controls with respect to the increase of calf volume after 5 min HUT. The acute (0-1 min) and the prolonged (1-5 min) phases of calf volume responses to HUT were also similar between patients and controls. No correlation was found between the degree of orthostatic hypotension and the orthostatic calf volume change in AF. In one patient an additional measurement was made before rising from bed in the early morning demonstrating a greater albeit small increase of calf volume upon HUT. Orthostatic fluid shifts at the level of the calf in AF are not augmented during the course of the day despite marked hypotension. However, a small increase of pooling may be expected when the patient first gets out of bed in the morning probably due to the absence of oedema.Paroxysmal Cerebral Disorder
The career orientation of final year teacher training students
The research was prompted by the assumption that the many problems in South African education
(e.g. continuous curiculum changes, insufficient in-service training and support, classroom
overcrowding, discipline problems,administrative paperwork, low teacher morale, high teacher
attrition rate, low societal status of the teaching profession) must have an adverse effect on the
career orientation of teacher training students. Our research was embedded in the theoretical
framework of eco-systemic theory (Bronfenbrenner 1990), through which we indicated how the teacher is surrounded and influenced by various societal systems in four levels of proximity: the
micro, meso, exo and macro levels. From these systems we established the conceptual framework,
in which we discussed negative forces on the teacher as these are eminent in societal expectations
about the teacher, the professional identity of the teacher and the retention rate in the teaching
profession. The discussion of these negative forces and their impact affirmed our initial assumption
and led to our research question: To what extent are teaching training students positively inclined
towards a career in teaching? This question implied attention to a) the career motivation, and b)
the moral values of the modern South African teaching training student.
The empirical study was conceptualised as a pilot project. We involved the full number of
final year teaching training students at one of the largest education faculties in South Africa,
namely at the University of Pretoria. The students (n = 403) were asked to complete a questionnaire
which focused inter alia on respondents’ exposure to daily news, reasons for choosing the education
career path, attitudes towards the teaching profession and medium to long term prospects in the
profession. Moral inclinations were also probed, e.g. with items on religion, discipline, language
of instruction, multicultural teaching and being a role model. The questionnaire findings were
verified in a focus group interview with five purposively selected respondents in the questionnaire
survey.
Our findings nullified our initial assumptions. Not only were the students strongly committed
to their chosen career, notwithstanding the questionable societal status of the teaching profession
and the formidable teaching challenges (of which they were apparently keenly aware), but they
also conveyed a strong message about moral values and the teacher’s role in modelling those in
and beyond the school. Our findings are prospective and certainly need verification on a broader
scale. We are also planning a follow-up study with the same respondents, once they have completed
two years of full time teaching.
The findings could serve as impetus for education management measures to ensure that
aspiring teachers’ level of commitment is sustainable. One of these measures could be an online
advice and counselling service for beginner teachers.Die navorsing het ontstaan uit die aanname dat die onderwysproblematiek in Suid-Afrika
(voortdurende kurrikulumwysigings, gebrekkige indiensopleiding, dissiplineprobleme, lae
beroepsmotivering onder onderwysers en gebrekkige aansien van die onderwysberoep) ’n
negatiewe uitwerking op die beroepsinstelling van onderwysstudente het. Vanuit die teoretiese
raamwerk wat gebruik is, naamlik Bronfenbrenner (1990) se ekosistemiese samelewingsmodel,
is die negatiewe kragte wat op die onderwys inwerk, nader toegelig. In die lig van die intensiteit
van hierdie kragte het die volgende as navorsingsvraag gedien: In welke mate het die huidige
onderwysstudent ’n positiewe beroepsingesteldheid? In ’n vraelysopname onder 403 finalejaar
onderwysstudente, is die aanvanklike aanname verkeerd bewys. Die vraelysrespondente was nie
alleen positief ingestel teenoor hul toekomstige loopbaan in die onderwys nie, maar hulle was
ook uitgesproke oor hul taak daarin as morele rolmodelle. Die positiewe aard van ons voorlopige
bevindings onderstreep alreeds die absolute noodsaaklikheid van onderwysbestuursmaatreëls om
die volhoubaarheid van beginneronderwysers se positiewe beroepsingesteldheid te verseker. ’n Elektroniese advies- en motiveringsdiens vir beginneronderwysers kan heel moontlik as eerste
en uitvoerbare projek hiertoe dien.http://www.journals.co.za/ej/ejour_akgees.htmlgv201
Polaris B, an optical companion of Polaris (alpha UMi) system: atmospheric parameters, chemical composition, distance and mass
We present an analysis of high-resolution spectroscopic observations of
Polaris B, the optical companion of the Polaris Ab system. The star has a
radial velocity V_r of -16.6km/s to -18.9km/s, and a projected rotational
velocity vsini=110 km/s. The derived atmospheric parameters are: Teff=6900K;
logg=4.3; V_t=2.5km/s. Polaris B has elemental abundances generally similar to
those of the Cepheid Polaris A (Usenko et al. 2005a), although carbon, sodium
and magnesium are close to the solar values. At a spectral type of F3V Polaris
B has a luminosity of 3.868L_sun, an absolute magnitude of +3.30mag, and a
distance of 109.5pc. The mass of the star is estimated to be 1.39M_sun, close
to a mass of 1.38+/-0.61M_sun for the recently-resolved orbital periods
companion Polaris Ab observed by Evans et al. (2007).Comment: 6 pages, 3 figures, 1 tabl
Polaris the Cepheid returns: 4.5 years of monitoring from ground and space
We present the analysis of 4.5 years of nearly continuous observations of the
classical Cepheid Polaris, which comprise the most precise data available for
this star. We have made spectroscopic measurements from ground and photometric
measurements from the WIRE star tracker and the SMEI instrument on the Coriolis
satellite. Measurements of the amplitude of the dominant oscillation (P = 4
days), that go back more than a century, show a decrease from 120 mmag to 30
mmag (V magnitude) around the turn of the millennium. It has been speculated
that the reason for the decrease in amplitude is the evolution of Polaris
towards the edge of the instability strip. However, our new data reveal an
increase in the amplitude by about 30% from 2003-2006. It now appears that the
amplitude change is cyclic rather than monotonic, and most likely the result of
a pulsation phenomenon. In addition, previous radial velocity campaigns have
claimed the detection of long-period variation in Polaris (P > 40 days). Our
radial velocity data are more precise than previous datasets, and we find no
evidence for additional variation for periods in the range 3-50 days with an
upper limit of 100 m/s. However, in the WIRE data we find evidence of variation
on time-scales of 2-6 days, which we interpret as being due to granulation.Comment: Accepted by ApJ. 8 pages. Quality of figures 1+3+7 degrade
Direct Detection of the Close Companion of Polaris with the Hubble Space Telescope
Polaris, the nearest and brightest classical Cepheid, is a single-lined
spectroscopic binary with an orbital period of 30 years. Using the High
Resolution Channel of the Advanced Camera for Surveys onboard the Hubble Space
Telescope (HST) at a wavelength of ~2255\AA, we have directly detected the
faint companion at a separation of 0\farcs17. A second HST observation 1.04 yr
later confirms orbital motion in a retrograde direction. By combining our two
measures with the spectroscopic orbit of Kamper and an analysis of the
Hipparcos and FK5 proper motions by Wielen et al., we find a mass for Polaris
Aa of 4.5^{+2.2}_{-1.4} M_\odot--the first purely dynamical mass determined for
any Cepheid. For the faint companion Polaris Ab we find a dynamical mass of
1.26^{+0.14}_{-0.07} M_\odot, consistent with an inferred spectral type of F6 V
and with the flux difference of 5.4 mag observed at 2255\AA. The magnitude
difference at the V band is estimated to be 7.2 mag. Continued HST observations
will significantly reduce the mass errors, which are presently still too large
to provide critical constraints on the roles of convective overshoot, mass
loss, rotation, and opacities in the evolution of intermediate-mass stars.
Our astrometry, combined with two centuries of archival measurements, also
confirms that the well-known, more distant (18") visual companion, Polaris B,
has a nearly common proper motion with that of the Aa,Ab pair. This is
consistent with orbital motion in a long-period bound system. The ultraviolet
brightness of Polaris B is in accordance with its known F3 V spectral type if
it has the same distance as Polaris Aa,Ab.Comment: 31 pages, 12 figures, 6 tables; accepted for publication in the
Astronomical Journa
Mg II h + k emission lines as stellar activity indicators of main sequence F-K stars
The main purpose of this study is to use the IUE spectra in the analysis of
magnetic activity of main sequence F-K stars. Combining IUE observations of
MgII and optical spectroscopy of Ca II, the registry of ctivity of stars can be
extended in time. We retrieved all the high-resolution spectra of F, G, and K
main sequence stars observed by IUE (i.e. 1623 spectra of 259 F to K dwarf
stars). We obtained the continuum surface flux near the Mg II h+k lines near
2800 \AA and the MgII line-core surface flux from the IUE spectra. We obtained
a relation between the mean continuum flux near the MgII lines with the colour
of the star. For a set of 117 nearly simultaneous observations of Mg II
and Ca II fluxes of 21 F5 to K3 main sequence stars, we obtained a colour
dependent relation between the Mount Wilson CaII S-index and the MgII emission
line-core flux. As an application of this calibration, we computed the Mount
Wilson index for all the dF to dK stars which have high resolution IUE spectra.
For some of the most frequently observed main sequence stars, we analysed the
Mount Wilson index S from the IUE spectra, together with the ones derived from
visible spectra. We confirm the cyclic chromospheric activity of epsilon Eri
(HD 22049) and beta Hydri (HD 2151), and we find a magnetic cycle in alpha Cen
B (HD 128621). Complete abstract in the paper.Comment: 10 pages, accepted for publication in Astronomy and Astrophysic
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