Helical Magnetorotational Instability in Magnetized Taylor-Couette Flow

Hollerbach and Rudiger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this "helical'' MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only). We confirm their results, calculate HMRI growth rates, and show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Growth rates are small and require large axial currents. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit. Also, keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of toroidal field lowers thresholds for instability even in finite cylinders.Comment: 16 pages, 2 figures, 1 table, submitted to PR

Direct electrophysiological evidence for the maintenance of retrieval orientations and the role of cognitive control

Retrieval orientations are memory states that bias retrieval towards specific memory contents. Many neuroimaging studies have examined the influence of retrieval orientations on stimulus processing, but very little direct evidence exists regarding the ongoing maintenance of orientations themselves. Participants completed two memory tasks with different retrieval goals. ERPs were time-locked to a pre-stimulus fixation asterisk and contrasted according to retrieval goals. Prestimulus ERPs elicited during the two retrieval tasks diverged at frontal electrode sites. These differences onset early and were sustained throughout the fixation-stimulus interval. The functional and spatiotemporal characteristics of this ERP effect comprise the first direct electrophysiological evidence of the ongoing maintenance of retrieval orientations throughout a task. Moreover, this effect was eliminated in participants who performed a stroop task prior to the memory tests, indicating that reserves of cognitive control play an important role in the maintenance of retrieval orientations throughout memory tasks

ERP evidence for the control of emotional memories during strategic retrieval

Neural evidence for the strategic retrieval of task-relevant ‘target’ memories at the expense of less relevant ‘nontarget’ memories has been demonstrated across a wide variety of studies. In ERP studies, this evidence consists of the ERP correlate of recollection (i.e. the ‘left parietal old/new effect’) being evident for targets and attenuated for nontargets. It is not yet known, however, whether this degree of strategic control can be extended to emotionally valenced words, or whether these items instead reactivate associated memories. The present study used a paradigm previously employed to demonstrate the strategic retrieval of neutral words (Herron & Rugg, Psychonomic Bulletin and & Review, 10(3), 703-–710, 2003b) to assess the effects of stimulus valence on behavioural and event-related potential (ERP) measures of strategic retrieval. While response accuracy and reaction times associated with targets were unaffected by valence, negative nontargets and new items were both associated with an elevated false alarm rate and longer RTs than their neutral equivalents. Both neutral and negative targets and nontargets elicited early old/new effects between 300 and 500 ms. Critically, whereas neutral and negative targets elicited robust and statistically equivalent left parietal old/new effects between 500 and 800 ms, these were absent for neutral and negative nontargets. A right frontal positivity associated with postretrieval monitoring was evident for neutral targets versus nontargets, for negative versus neutral nontargets, and for targets versus new items. It can therefore be concluded that the recollection of negatively valenced words is subject to strategic control during retrieval, and that postretrieval monitoring processes are influenced by emotional valence

Development of biostereometric experiments

The stereometric camera was designed for close-range techniques in biostereometrics. The camera focusing distance of 360 mm to infinity covers a broad field of close-range photogrammetry. The design provides for a separate unit for the lens system and interchangeable backs on the camera for the use of single frame film exposure, roll-type film cassettes, or glass plates. The system incorporates the use of a surface contrast optical projector

Stereometric body volume measurement

The following studies are reported: (1) effects of extended space flight on body form of Skylab astronauts using biostereometrics; (2) comparison of body volume determinations using hydrostatic weighing and biostereometrics; and (3) training of technicians in biostereometric principles and procedures

Investigating the use of chloroquine as antineoplastic therapy

Chloroquine (CQ) is an oral lysosomotropic agent routinely used as an anti-malarial drug (Espina & Liotta, 2013). In recent years, it has been discovered that CQ also possesses anticancer effects, potentially due to the drug’s inhibition of autophagy (Kimura, Takabatake, Takahashi, & Isaka, 2012). Autophagy is a normal cellular pathway that allows for the degradation of cytoplasmic contents. In cancer cells autophagy can also serve as a pro-survival pathway under stressful metabolic conditions, ultimately promoting the survival of malignant cells (Sui et al., 2013). Therefore, in recent years CQ has been speculated as a potential antineoplastic therapy. When administered in conjunction with typical chemotherapeutic agents, CQ also has the potential to decrease acquired drug resistance, enhance the efficacy of chemotherapeutic agents, and prevent pre-invasive cells from transitioning to invasive cells (Espina & Liotta, 2013). However, this potential antineoplastic effect has been observed to vary somewhat between cancer types and phases of tumorigenesis, and the precise antineoplastic mechanism of CQ is not clearly understood (Sui et al., 2013). The purpose of this literature review was to evaluate the current evidence in order to compare the efficacy and safety of the use of CQ as an antineoplastic agent in various types of cancer. Additionally, the conjectured antineoplastic effects of CQ discussed in each reviewed study were compared in order to gain greater understanding of the probable mechanism of action of CQ in cancer cells

Preparation breeds success: Brain activity predicts remembering

Successful retrieval of episodic information is thought to involve the adoption of memory states that ensure that stimulus events are treated as episodic memory cues (retrieval mode) and which can bias retrieval toward specific memory contents (retrieval orientation). The neural correlates of these memory states have been identified in many neuroimaging studies, yet critically there is no direct evidence that they facilitate retrieval success. We cued participants before each test item to prepare to complete an episodic (retrieve the encoding task performed on the item at study) or a non-episodic task. Our design allowed us to separate event-related potentials (ERPs) elicited by the preparatory episodic cue according to the accuracy of the subsequent memory judgment. We predicted that a correlate of retrieval orientation should be larger in magnitude preceding correct source judgments than that preceding source errors. This hypothesis was confirmed. Preparatory ERPs at bilateral frontal sites were significantly more positive-going when preceding correct source judgments than when preceding source errors or correct responses in a non-episodic baseline task. Furthermore this effect was not evident prior to recognized items associated with incorrect source judgments. This pattern of results indicates a direct contribution of retrieval orientation to the recovery of task-relevant information and highlights the value of separating preparatory neural activity at retrieval according to subsequent memory accuracy. Moreover, at a more general level this work demonstrates the important role of pre-stimulus processing in ecphory, which has remained largely neglected to date