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PubMed2003

Convective heat transport in a rotating fluid layer of infinite Prandtl number: optimum fields and upper bounds on Nusselt number.

By means of the Howard-Busse method of the optimum theory of turbulence we investigate numerically upper bounds on convective heat transport for the case of infinite fluid layer with stress-free vertical boundaries rotating about a vertical axis. We discuss the case of infinite Prandtl number, 1-alpha solution of the obtained variational problem and optimum fields possessing internal, intermediate, and boundary layers. We investigate regions of Rayleigh and Taylor numbers R and Ta, where no analytical bounds can be derived, and compare the analytical and numerical bounds for these regions of R and Ta where such comparison is possible. The increasing rotation has a different influence on the rescaled optimum fields of velocity w(1), temperature theta(1) and the vertical component of the vorticity f(1). The increasing Ta for fixed R leads to vanishing of the boundary layers of w(1) and theta(1). Opposite to this, the increasing Ta leads first to a formation of boundary layers of the field f(1) but further increasing the rotation causes vanishing of these boundary layers. We obtain optimum profiles of the horizontal averaged total temperature field which could be used as hints for construction of the background fields when applying Doering-Constantin method to the problems of rotating convection. The wave number alpha(1) corresponding to the optimum fields follows the asymptotic relationship alpha(1)=(R/5)(1/4) for intermediate Rayleigh numbers. However, when R becomes large with respect to Ta, after a transition region, the power law for alpha(1) becomes close to the power law for the case without rotation. The Nusselt number Nu is close to the nonrotational bound 0.32R(1/3) for the case of large R and small Ta. Nu decreases with increasing Taylor number. Thus, the upper bounds reflect the tendency of inhibiting thermal convection by increasing rotation for a fixed Rayleigh number. For the regions of Rayleigh and Taylor numbers where the numerical and asymptotic bounds on Nu can be compared, the numerical bounds are about 70% lower than the asymptotic bounds.

Journal Article↗
PubMed2003

Bifurcation and stability analysis of rotating chemical spirals in circular domains: boundary-induced meandering and stabilization.

Recent experimental and model studies have revealed that the domain size may strongly influence the dynamics of rotating spirals in two-dimensional pattern forming chemical reactions. Hartmann et al. [Phys. Rev. Lett. 76, 1384 (1996)], report a frequency increase of spirals in circular domains with diameters substantially smaller than the spiral wavelength in a large domain for the catalytic NO+CO reaction on a microstructured platinum surface. Accompanying simulations with a simple reaction-diffusion system reproduced the behavior. Here, we supplement these studies by a numerical bifurcation and stability analysis of rotating spirals in a simple activator-inhibitor model. The problem is solved in a co-rotating frame of reference. No-flux conditions are imposed at the boundary of the circular domain. At large domain sizes, eigenvalues and eigenvectors very close to those corresponding to infinite medium translational invariance are observed. Upon decrease of domain size, we observe a simultaneous change in the rotation frequency and a deviation of these eigenvalues from being neutrally stable (zero real part). The latter phenomenon indicates that the translation symmetry of the spiral solution is appreciably broken due to the interaction with the (now nearby) wall. Various dynamical regimes are found: first, the spiral simply tries to avoid the boundary and its tip moves towards the center of the circular domain corresponding to a negative real part of the "translational" eigenvalues. This effect is noticeable at a domain radius of R<R(cr,1). The spiral subsequently exhibits an oscillatory instability: the tip trajectory displays a meandering motion, which may be characterized as boundary-induced spiral meandering. A systematic study of the spiral rotation as a function of a control parameter and the domain size reveals that the meandering instability in large domains becomes suppressed, and the spiral rotation becomes rigid, at a critical radius R(cr,0). Boundary-induced meandering arises below a second critical radius R(cr,2)<R(cr,0).

Journal Article↗
PubMed2006

Polygons on a rotating fluid surface.

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water, we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat [J. M. Lopez, J. Fluid Mech. 502, 99 (2004). We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate.

Journal Article↗
PubMed1966

Role of Indole-3-acetic Acid in Modification of Geotropic Responses in Clinostat Rotated Avena Seedlings.

Oat seedlings were grown in a sand medium on clinostats with horizontal axes of rotation to nullify the directional component of the gravity-force vector. Coleoptile segments from such seedlings showed an enhanced absorption of apically applied exogenous auxin (indole-3-acetic acid), compared to segments from vertically rotated or stationary controls. Absorption of basally applied auxin and auxin transport were unaffected by the gravity treatments. Horizontal rotation did not materially change the amount of auxin produced and transported from excised coleoptile tips: however, plants so rotated showed an enhanced curvature response to unilaterally applied auxin.Collectively, these experiments indicate that enhanced plant responses to horizontal clinostat rotation, where rates of rotation are sufficient to nullify the directional component of the gravity-force vector, are caused primarily by increases in metabolism and not by a modification of auxin availability. These data do not support recently advanced hypotheses that the polarity of auxin transport is based on gravitational sedimentation of cell inclusions.

Journal Article↗
PubMed1970

Choice of rotation rate for the horizontal clinostat.

A series of nine rates of rotation of the clinostat were tested to determine optimal and acceptable conditions for simulating weightlessness in plants. Young seedlings of wheat (Triticum aestivum L.) developed roots and coleoptiles of equal lengths and with the same orientation angles over a range of rotation rates from 0.25 to 480 minutes per revolution. Rates from 0.25 to 3 minutes per revolution provided for maximal epinastic curvatures of leaves and branches of Coleus blumei Benth. except for a reduced mean curvature of branches at 0.25 minute per revolution, due probably to physical disturbances in their growth. Smaller epinastic curvatures developed in both leaves and branches rotated at 15 minutes per revolution or more slowly. Indoleacetic acid-2-(14)C was used for measurements of extractable radioactivity in determining the reason for smaller curvatures of Coleus branches and tomato (Lycopersicon esculentum Mill.) leaves at the rotation rate of 60 minutes per revolution than at 1 minute per revolution. The cause was determined to be movement of some auxin from the upper into the lower side of a plagiotropic leaf or branch under the transient influence of gravity during rotation on the slower clinostat. A rotation period of 1 to 3 minutes was found to be acceptable for most plants.

Journal Article↗
PubMed2001

Surface acoustic waves propagating over a rotating piezoelectric half-space.

Surface acoustic waves (SAW) propagating over a piezoelectric half-space rotating at a constant angular rate about a fixed axis are analyzed using the linear theory of piezoelectricity, including Coriolis and centrifugal forces. Rotation sensitivity, the rotation induced change of wave speed, is studied. The dependence of the rotation sensitivity on the orientation of the rotation axis and the orientation of the material is examined. Numerical results for polarized ceramics PZT-5H are presented to show the detailed characteristics of the rotation sensitivity. The implications of the numerical results are discussed for different applications.

Journal Article↗
PubMed2006

Rotation forest: A new classifier ensemble method.

We propose a method for generating classifier ensembles based on feature extraction. To create the training data for a base classifier, the feature set is randomly split into K subsets (K is a parameter of the algorithm) and Principal Component Analysis (PCA) is applied to each subset. All principal components are retained in order to preserve the variability information in the data. Thus, K axis rotations take place to form the new features for a base classifier. The idea of the rotation approach is to encourage simultaneously individual accuracy and diversity within the ensemble. Diversity is promoted through the feature extraction for each base classifier. Decision trees were chosen here because they are sensitive to rotation of the feature axes, hence the name "forest." Accuracy is sought by keeping all principal components and also using the whole data set to train each base classifier. Using WEKA, we examined the Rotation Forest ensemble on a random selection of 33 benchmark data sets from the UCI repository and compared it with Bagging, AdaBoost, and Random Forest. The results were favorable to Rotation Forest and prompted an investigation into diversity-accuracy landscape of the ensemble models. Diversity-error diagrams revealed that Rotation Forest ensembles construct individual classifiers which are more accurate than these in AdaBoost and Random Forest, and more diverse than these in Bagging, sometimes more accurate as well.

Algorithms↗
PubMed1997

Internal rotation gait: a compensatory mechanism to restore abduction capacity decreased by bone deformity.

Children with excessive femoral anteversion frequently walk with abnormal internal rotation of the hip. The authors hypothesized that excessive anteversion decreases the abduction moment arm of the gluteus medius and that this moment arm is restored with internal rotation; hence internal rotation may be a compensatory mechanism to preserve abduction capacity. To test this hypothesis a three-dimensional computer model of an adult lower limb was developed to determine how changes in femoral anteversion angle, neck-shaft angle, and hip internal rotation angle affect the abduction moment arm of the gluteus medius. Analysis of the model revealed that anteversion and valgus deformities of the femur can decrease the abduction moment arm of the gluteus medius substantially. In particular, increasing the anteversion angle of the model by 30 to 40 degrees caused a 40 to 50% decrease in the abduction moment arm of the gluteus medius - enough to impair walking. Internal rotation of the hip by 30 degrees restored the abduction moment arm of the gluteus medius to within 5% of the moment arm of the model in its normal, undeformed state. These results support the authors' hypothesis and are consistent with the theory that internal rotation may be a compensatory mechanism adopted by children with femoral deformities to achieve the abduction moment arm needed for walking.

Biomechanical Phenomena↗
PubMed1989

Brain potentials during selective attention, memory search, and mental rotation.

Event-related potentials were measured in a task that combined the classic selective attention paradigm with memory search and mental rotation paradigms. Subjects were required to attend to stimulus letters in one color and to ignore stimuli in a different color. Within the attended category subjects searched for target letters from a prememorized set (the memory set) and indicated whether they were presented normally or in mirror-image. Letters in all stimulus categories were presented randomly in either their upright position or rotated over 60 degrees, 120 degrees, or 180 degrees. The event-related potentials showed that the earliest effect of attending to color was a positivity at the anterior electrodes and a negativity at Oz (onset about 150 ms), followed by the enhancement of a central N2 component (N2b, onset about 220 ms). The early effect is thought to reflect selective processing of elementary stimulus features, the later N2b the covert orienting of attention. A later, prolonged central negativity elicited by attended stimuli covaried with the duration of the memory search process. Target detection resulted in a parietal P3b component, and also in an earlier negativity (in the range approximately 200-300 ms) to both attended and unattended targets, suggesting an early preattentive target classification. There were two effects of the rotation of stimuli. First there was an early occipital effect (about 200-300 ms), irrespective of attention and stimulus categories. It was argued that this effect reflected the preattentive identification of the orientation of the stimulus letters. A later (onset about 350-400 ms) parietal effect consisted of an increase in negativity as a function of the angle over which letters were rotated. This prolonged negativity had a later onset latency than the search-related negativity, and was restricted to the event-related potentials to target letters in the attended input channel. It was suggested that this component is the manifestation of a mental rotation process. It was argued that rotation-related negativity and memory search-related activity reflect operations in distinct working memory subsystems.

Adult↗
PubMed2004

Teaching and learning in an 80-hour work week: a novel day-float rotation for medical residents.

The 80-hour workweek limit for residents provides an opportunity for residency directors to creatively innovate their programs. Our novel day-float rotation augmented both the educational structure within the inpatient team setting and the ability for house staff to complete their work within the mandated limits. Descriptive evaluation of the rotation was performed through an end-of-rotation questionnaire. The average length of the ward residents' work week was quantified before and after the rotation's implementation. Educational portfolios and mentored peer-teaching opportunities enriched the rotation. As measured by our evaluation, this new rotation enhanced learning and patient care while reducing work hours for inpatient ward residents.

Internal Medicine↗
PubMed2006

Effect of the inpatient general medicine rotation on student pursuit of a generalist career.

BACKGROUND: Entry into general internal medicine (GIM) has declined. The effect of the inpatient general medicine rotation on medical student career choices is uncertain. OBJECTIVE: To assess the effect of student satisfaction with the inpatient general medicine rotation on pursuit of a career in GIM. DESIGN: Multicenter cohort study. PARTICIPANTS: Third-year medical students between July 2001 and June 2003. MEASUREMENTS: End-of-internal medicine clerkship survey assessed satisfaction with the rotation using a 5-point Likert scale. Pursuit of a career in GIM defined as: (1) response of "Very Likely" or "Certain" to the question "How likely are you to pursue a career in GIM?"; and (2) entry into an internal medicine residency using institutional match data. RESULTS: Four hundred and two of 751 (54%) students responded. Of the student respondents, 307 (75%) matched in the 2 years following their rotations. Twenty-eight percent (87) of those that matched chose an internal medicine residency. Of these, 8% (25/307) were pursuing a career in GIM. Adjusting for site and preclerkship interest, overall satisfaction with the rotation predicted pursuit of a career in GIM (odds ratio [OR] 3.91, P<.001). Although satisfaction with individual items did not predict pursuit of a generalist career, factor analysis revealed 3 components of satisfaction (attending, resident, and teaching). Adjusting for preclerkship interest, 2 factors (attending and teaching) were associated with student pursuit of a career in GIM (P<.01). CONCLUSIONS: Increased satisfaction with the inpatient general medicine rotation promotes pursuit of a career in GIM.

Career Choice↗
PubMed1992

Geriatric education. Part I: Efficacy of a mandatory clinical rotation for fourth year medical students.

OBJECTIVES: To describe the curriculum of a mandatory, fourth-year geriatrics clerkship and assess its impact on medical students' knowledge of geriatric medicine and attitudes toward the elderly. DESIGN: One group, before/after trial. SETTING: Mount Sinai School of Medicine of the City University of New York. PARTICIPANTS: Entire fourth year class of medical students (n = 127). INTERVENTION: Four-week-long clinical geriatrics clerkship. MEASUREMENTS: Pre- and post-rotation: test of knowledge; Aging Semantic Differential (ASD) attitude scale; Modified Maxwell-Sullivan attitude scale; questionnaire. MAIN RESULTS: Seventy percent of students found the rotation to be educationally valuable; however, only one-third of students would have taken the clerkship had it not been required. Mean geriatric knowledge score increased by 18.7% (P less than 0.001). Mean ASD attitude score did not change significantly (130.5 +/- 19.2 pre-rotation versus 126.6 +/- 18.8 post-rotation, P = 0.15), but students started the rotation with a neutral attitude. Over 90% of students agreed they would welcome elderly into their future practice. CONCLUSION: If a national curricular goal is to improve medical students' knowledge of geriatric medicine, required rather than elective rotations may be in order.

Adult↗
PubMed1996

Prospective evaluation of emergency medicine instruction for rotating first-postgraduate-year residents.

OBJECTIVE: To determine whether either bedside teaching alone (group A) or bedside teaching with written course materials (group B) improved written examination scores, satisfaction with the rotation, or clinical grades of rotating PGY1 residents. METHODS: A prospective, controlled educational trial was conducted. Sixty-five PGY1 residents from diverse specialties rotated in the ED for one month over a ten-month study period, and were included in the study. The PGY1 residents were assigned to group by month of rotation. All the PGY1 residents received unstructured bedside teaching by emergency medicine (EM) residents and faculty. In addition, group B received written course materials on day 1. RESULTS: Mean posttest scores were higher than mean pretest scores for the interns considered as a whole (p < 0.0001), but mean pretest, posttest, and clinical grades were comparable across instructional groups. Mean satisfaction ratings were higher for group A than for group B (p < 0.015). The interns specializing in EM achieved higher mean test scores (p < 0.013) and clinical grades (p < 0.003) than did the interns specializing in another medical specialty. CONCLUSION: Both instructional methods were associated with improved written test performance. Written course materials did not augment bedside teaching in terms of test scores, clinical grades, or satisfaction with the rotation. At a university-based, high-volume ED, bedside teaching offers educational benefit to rotating PGY1 residents that may not be augmented by written course materials.

Curriculum↗
PubMed2001

Some current research in rotating-disc systems.

Rotating-disc systems are used to model the flow and heat transfer that occurs inside the cooling-air systems of gas-turbine engines. In this paper, recent computational and experimental research in three systems is discussed: rotor-stator systems, rotating cavities with superposed flow and buoyancy-induced flow in a rotating cavity. Discussion of the first two systems concentrates respectively on pre-swirl systems and rotating cavities with a peripheral inflow and outflow of cooling air. Buoyancy-induced flow in a rotating cavity is one of the most difficult problems facing computationalists and experimentalists, and there are similarities between the circulation in the Earth's atmosphere and the flow inside gas-turbine rotors. For this case, results are presented for heat transfer in sealed annuli and in rotating cavities with an axial throughflow of cooling air.

Journal Article↗
PubMed1985

Rotation of the cell nucleus in living cells: a quantitative analysis.

Nuclear rotation is observed in a variety of cell types. However, few quantitative analyses are reported and the significance of this phenomenon is still unclear. To investigate this type of nuclear movement, we performed a quantitative analysis in mouse L-929 fibroblasts, a cell line chosen since it displays a high nuclear rotational activity. Analyses were performed using time-lapse microcinematography. The relationship between nuclear rotation and other cellular phenomena such as the cell cycle and locomotion were studied. Then, we investigated the rotation in a population of sister cells to study whether it is genetically determined. Finally, we performed a qualitative analysis of nuclear rotation in different cultured cell lines. Results show that nuclear rotations preferentially occur during the phases of the cell cycle which surround mitosis.

Animals↗
PubMedDate not supplied

Reconstruction for fan beam with an angular-dependent displaced center-of-rotation.

A convolutional backprojection algorithm is derived for a fan beam geometry that has an angular-dependent displacement in its center-of-rotation from the midline of the fan beam. In both x-ray computed tomography and single photon emission computed tomography, misalignment can occur when the mechanical center-of-rotation is not colinear with midline of the fan beam. In some cases the shift in the center-of-rotation is constant for every angle, whereas, in other cases it varies with angular position. Standard reconstruction algorithms, which directly filter and backproject the fan beam data without rebinning into parallel beam geometry, have been derived for a geometry having its center-of-rotation at the midline of the fan beam. However, in the case of any misalignment of the center-of-rotation, if these conventional reconstruction algorithms are used to reconstruct the fan beam projections, structured artifacts and a loss of resolution will result. Simulations are performed that illustrate these artifacts and demonstrate how the new algorithm corrects for this misalignment. A method for estimating the parameters of the fan beam geometry, including the angular-dependent shift in the center-of-rotation, is also described.

Algorithms↗
PubMed1999

Proposition: a pregnant resident physician should be excused from training rotations such as angiography and nuclear medicine because of the potential exposure of the fetus.

It has been reasonably well documented that a pregnant resident physician can assume radiology rotations, including higher-exposure rotations such as angiography and nuclear medicine, without exposing the fetus to radiation levels that exceed national and international guidelines. Hence, many medical physicists support the contention that rotations should not be altered because a resident is pregnant. On the other hand, many if not most physicists subscribe to the ALARA (as low as reasonably achievable) principle, especially in cases of fetal exposure where increased radiation susceptibility is combined with an inability to decide for one-self. In addition, altered rotations usually can be accommodated by swapping rotations with other residents, with the pregnant resident taking high exposure rotations after delivery of the child. Policies on this issue vary among institutions, possibly because medical physicists have not come to closure on the issue. This issue of Point/Counterpoint is directed toward that objective.

Education, Medical, Graduate↗
PubMed1995

A Starter Culture Rotation Strategy Incorporating Paired Restriction/ Modification and Abortive Infection Bacteriophage Defenses in a Single Lactococcus lactis Strain.

Three derivatives of Lactococcus lactis subsp. lactis NCK203, each with a different pair of restriction/ modification (R/M) and abortive infection (Abi) phage defense systems, were constructed and then rotated in repeated cycles of a milk starter culture activity test (SAT). The rotation proceeded successfully through nine successive SATs in the presence of phage and whey containing phage from previous cycles. Lactococcus cultures were challenged with 2 small isometric-headed phages, (phi)31 and ul36, in one rotation series and with a composite of 10 industrial phages in another series. Two native lactococcal R(sup+)/M(sup+) plasmids, pTRK68 and pTRK11, and one recombinant plasmid, pTRK308, harboring a third distinct R/M system were incorporated into three NCK203 derivatives constructed separately for the rotation. The R(sup+)/M(sup+) NCK203 derivatives were transformed with high-copy-number plasmids encoding four Abi genes, abiA, abiC, per31, and per50. Various Abi and R/M combinations constructed in NCK203 were evaluated for their effects on cell growth, level of phage resistance, and retardation of phage development during repeated cycles of the SAT. The three NCK203 derivatives chosen for use in the SAT exhibited additive effects of the R/M and Abi phenotypes against sensitive phages. In such combinations, phage escaping restriction are prevented from completing their infective cycle by an abortive response that kills the host cell. The rotation series successfully controlled modified, recombinant, and mutant phages which were resistant to any one of the individual defense systems by presenting a different set of R/M and Abi defenses in the next test of the rotation.

Journal Article↗