Cutting and Shuffling a Line Segment: Mixing by Interval Exchange Transformations

We present a computational study of finite-time mixing of a line segment by cutting and shuffling. A family of one-dimensional interval exchange transformations is constructed as a model system in which to study these types of mixing processes. Illustrative examples of the mixing behaviors, including pathological cases that violate the assumptions of the known governing theorems and lead to poor mixing, are shown. Since the mathematical theory applies as the number of iterations of the map goes to infinity, we introduce practical measures of mixing (the percent unmixed and the number of intermaterial interfaces) that can be computed over given (finite) numbers of iterations. We find that good mixing can be achieved after a finite number of iterations of a one-dimensional cutting and shuffling map, even though such a map cannot be considered chaotic in the usual sense and/or it may not fulfill the conditions of the ergodic theorems for interval exchange transformations. Specifically, good shuffling can occur with only six or seven intervals of roughly the same length, as long as the rearrangement order is an irreducible permutation. This study has implications for a number of mixing processes in which discontinuities arise either by construction or due to the underlying physics.Comment: 21 pages, 10 figures, ws-ijbc class; accepted for publication in International Journal of Bifurcation and Chao

Potential Vorticity Evolution of a Protoplanetary Disk with An Embedded Protoplanet

We present two-dimensional inviscid hydrodynamic simulations of a protoplanetary disk with an embedded planet, emphasizing the evolution of potential vorticity (the ratio of vorticity to density) and its dependence on numerical resolutions. By analyzing the structure of spiral shocks made by the planet, we show that progressive changes of the potential vorticity caused by spiral shocks ultimately lead to the excitation of a secondary instability. We also demonstrate that very high numerical resolution is required to both follow the potential vorticity changes and identify the location where the secondary instability is first excited. Low-resolution results are shown to give the wrong location. We establish the robustness of a secondary instability and its impact on the torque onto the planet. After the saturation of the instability, the disk shows large-scale non-axisymmetry, causing the torque on the planet to oscillate with large amplitude. The impact of the oscillating torque on the protoplanet's migration remains to be investigated.Comment: 17 pages total with 9 figures (Fig.4,5,9 are in .jpg), accepted to Ap

Changes in auditory perceptions and cortex resulting from hearing recovery after extended congenital unilateral hearing loss

Monaural hearing induces auditory system reorganization. Imbalanced input also degrades time-intensity cues for sound localization and signal segregation for listening in noise. While there have been studies of bilateral auditory deprivation and later hearing restoration (e.g. cochlear implants), less is known about unilateral auditory deprivation and subsequent hearing improvement. We investigated effects of long-term congenital unilateral hearing loss on localization, speech understanding, and cortical organization following hearing recovery. Hearing in the congenitally affected ear of a 41 year old female improved significantly after stapedotomy and reconstruction. Pre-operative hearing threshold levels showed unilateral, mixed, moderately-severe to profound hearing loss. The contralateral ear had hearing threshold levels within normal limits. Testing was completed prior to, and three and nine months after surgery. Measurements were of sound localization with intensity-roved stimuli and speech recognition in various noise conditions. We also evoked magnetic resonance signals with monaural stimulation to the unaffected ear. Activation magnitudes were determined in core, belt, and parabelt auditory cortex regions via an interrupted single event design. Hearing improvement following 40 years of congenital unilateral hearing loss resulted in substantially improved sound localization and speech recognition in noise. Auditory cortex also reorganized. Contralateral auditory cortex responses were increased after hearing recovery and the extent of activated cortex was bilateral, including a greater portion of the posterior superior temporal plane. Thus, prolonged predominant monaural stimulation did not prevent auditory system changes consequent to restored binaural hearing. Results support future research of unilateral auditory deprivation effects and plasticity, with consideration for length of deprivation, age at hearing correction, degree and type of hearing loss

Early and Rapid Development of Bronchiolitis Obliterans Syndrome after Allogeneic Hematopoietic Cell Transplantation

Bronchiolitis obliterans (BO) is a form of graft-versus-host disease (GVHD) in the lung and manifests as moderate to severe airflow obstruction after hematopoietic stem cell transplantation (HCT). New-onset airflow obstruction on spirometry is considered diagnostic of bronchiolitis obliterans syndrome (BOS). BOS affects about 5% of all HCT recipients. In general, BO is thought of as a late complication of HCT, usually occurring after day 100 post-transplantation. However, the onset of airflow obstruction can be rapid and is most often irreversible even with treatment. We describe a patient who rapidly developed severe airflow obstruction less than one month after transplantation following the development of upper airway symptoms. Despite aggressive immunosuppression, the patient had no improvement in airflow obstruction. We hypothesize that early screening and treatment may help prevent BOS after HCT

An Organizational Change Perspective

We present the concept of organizational misfit as a complement to multi-contingency theory fit concepts for organizational performance. Firms with misfits have opportunity losses that firms without misfits do not suffer. Using data from 232 small and medium sized Danish firms, we confirm the hypotheses that firms with either or both situational and contingency misfits have lower performance increases than firms without misfits. Further, a firm may not obtain increased performance from the elimination of misfits piecemeal, but will obtain significant nonlinear positive increases when misfits are fixed within a holistic or systems approach

Border crossings in the African travel narratives of Ibn Battuta, Richard Burton and Paul Theroux

This article compares the representation of African borders in the 14th-century travelogue of Ibn Battuta, the 19th-century travel narrative of Richard Burton and the 21st-century travel writing of Paul Theroux. It examines the mutually constitutive relationship between conceptions of literal territorial boundaries and the figurative boundaries of the subject that ventures across borders in Africa. The border is seen as a liminal zone which paradoxically separates and joins spaces. Accounts of border crossings in travel writing from different periods suggest the historicity and cultural specificity of conceptions of geographical borders, and the way they index the “boundaries” of the subjects who cross them. Tracing the transformations in these conceptions of literal and metaphorical borders allows one to chart the emergence of the dominant contemporary idea of “Africa” as the inscrutable, savage continent

Complete replication of hepatitis C virus in cell culture.

Many aspects of the hepatitis C virus (HCV) life cycle have not been reproduced in cell culture, which has slowed research progress on this important human pathogen. Here, we describe a full-length HCV genome that replicates and produces virus particles that are infectious in cell culture (HCVcc). Replication of HCVcc was robust, producing nearly 10(5) infectious units per milliliter within 48 hours. Virus particles were filterable and neutralized with a monoclonal antibody against the viral glycoprotein E2. Viral entry was dependent on cellular expression of a putative HCV receptor, CD81. HCVcc replication was inhibited by interferon-alpha and by several HCV-specific antiviral compounds, suggesting that this in vitro system will aid in the search for improved antivirals

Tension and Resistance to Change Organizational Climate: Managerial Implications for a Fast Paced World

Climate is the atmosphere of the organization, a “relatively enduring quality of the internal environment of an organization, which is experienced by its members and influences their behavior.” The organizational climate can be measured in terms of trust, morale, conflict, equity in rewards, leader credibility, resistance to change and scapegoating. Using a factor analysis, we found that the organizational climate can be described in two dimensions: “tension” and the resistance to change for a group of 245 Danish companies. High tension involves strained relationships, stress and a balance of the combined factors. High resistance to change is a preference for tomorrow to be like today. Change management has a long history and rests fundamentally upon Lewin’s three phases: unfreeze, change and re-freeze. More recently, change management is seen as sensemaking and the creation of an organizational reality in which change is more usual and continuous. Using the competing values framework, four organizational climates emerge: S internal process, which is high on tension and resistance to change, S rational goal, which is high on tension and low on resistance to change, S developmental, which is low on tension and low on resistance to change, and S group, which is low on tension and high on resistance to change. The managerial implications are complex For a fast paced world, the resistance to change must be low. Lewinian episodic change is difficult, slow and costly. Continuous change can be managed, where change becomes the norm of the organization. However, tension does not have to be low. Individuals may prefer a low tension organization, but it may not be necessary for a fast paced world. Further, since the two dimensions are independent, managers cannot reduce tension as a means to reduce the resistance to change