• Computed stabilization for a giant fullerene endohedral: Y2C2@C1(1660)-C108

      Slanina, Zdeněk; Uhlík, Filip; Pan, Changwang; Akasaka, Takeshi; Lu, Xing; Adamowicz, Ludwik; Univ Arizona, Dept Chem & Biochem (Elsevier, 2018-10-16)
    • Model-independent Test of the Cosmic Distance Duality Relation

      Ruan, Cheng-Zong; Melia, Fulvio; Zhang, Tong-Jie; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (IOP PUBLISHING LTD, 2018-10-08)
      A validation of the cosmic distance duality (CDD) relation, h() ( ) () () z zdz dz º+ = 1 A L 1 2 , coupling the luminosity (dL) and angular-diameter (dA) distances, is crucial because its violation would require exotic new physics. We present a model-independent test of the CDD, based on strong lensing and a reconstruction of the H II galaxy Hubble diagram using Gaussian processes, to confirm the validity of the CDD at a very high level of confidence. Using parameterizations h( )z z = +1 h0 and h( )z zz =+ + 1 h h 1 2 2, our best-fit results are h = - + 0.0147 0 0.066 0.056, and h = - + 0.1091 1 0.1568 0.1680 and h = - - + 0.0603 2 0.0988 0.0999, respectively. In spite of these strong constraints, however, we also point out that the analysis of strong lensing using a simplified single isothermal sphere (SIS) model for the lens produces some irreducible scatter in the inferred CDD data. The use of an extended SIS approximation, with a power-law density structure, yields very similar results, but does not lessen the scatter due to its larger number of free parameters, which weakens the best-fit constraints. Future work with these strong lenses should therefore be based on more detailed ray-tracing calculations to determine the mass distribution more precisely
    • Cosmological tests with the joint lightcurve analysis

      Melia, F.; Wei, J.-J.; Maier, R.S.; Wu, X.-F.; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron; Univ Arizona, Dept Phys; Univ Arizona, Dept Math; Univ Arizona, Statistics Program (EPL ASSOCIATION, 2018-10-05)
      We examine whether a comparison between wCDM and $R_{\textrm{h}}=ct$ using merged Type-Ia SN catalogs produces results consistent with those based on a single homogeneous sample. Using the Betoule et al. (Astron. Astrophys., 568 (2014) 22). Joint Lightcurve Analysis (JLA) of a combined sample of 613 events from SNLS and SDSS-II, we estimate the parameters of the two models and compare them. We find that the improved statistics can alter the model selection in some cases, but not others. In addition, based on the model fits, we find that there appears to be a lingering systematic offset of ~0.04–0.08 mag between the SNLS and SDSS-II sources, in spite of the cross-calibration in the JLA. Treating wCDM, ΛCDM and $R_{\textrm{h}}=ct$ as separate models, we find in an unbiased pairwise statistical comparison that the Bayes Information Criterion (BIC) favors the $R_{\textrm{h}}=ct$ Universe with a likelihood of $82.8\%$ vs. $17.2\%$ for wCDM, but the ratio of likelihoods is reversed ($16.2\%$ vs. $83.8\%$ ) when $w_{\textrm{de}}=-1$ (i.e., ΛCDM) and strongly reversed ($1.0\%$ vs. $99.0\%$ ) if in addition k = 0 (i.e., flat ΛCDM). We point out, however, that the value of k is a measure of the net energy (kinetic plus gravitational) in the Universe and is not constrained theoretically, though some models of inflation would drive $k\rightarrow 0$ due to an expansion-enforced dilution. Since we here consider only the basic ΛCDM model, the value of k needs to be measured and, therefore, the pre-assumption of flatness introduces a significant bias into the BIC.
    • Constrained vs unconstrained labor supply: the economics of dual job holding

      Choe, Chung; Oaxaca, Ronald L.; Renna, Francesco; Univ Arizona, Dept Econ, Eller Coll Management (SPRINGER, 2018-10)
      This paper develops a unified model of dual and unitary job holding based on a Stone-Geary utility function. The model incorporates both constrained and unconstrained labor supply. Panel data methods are adapted to accommodate unobserved heterogeneity and multinomial selection into six mutually exclusive labor supply regimes. We estimate the wage and income elasticities arising from selection and unobserved heterogeneity as well as from the Stone-Geary Slutsky equations. The labor supply model is estimated with data from the British Household Panel Survey 1991-2008. Among dual job holders, our study finds that the Stone-Geary income and wage elasticities are much larger for labor supply to the second job compared with the main job. When the effects of selection and unobserved heterogeneity are taken account of, the magnitudes of these elasticities on the second job tend to be significantly reduced.
    • Highly porous defective carbons derived from seaweed biomass as efficient electrocatalysts for oxygen reduction in both alkaline and acidic media

      Hao, Yajuan; Zhang, Xu; Yang, Qifeng; Chen, Kai; Guo, Jun; Zhou, Dongying; Feng, Lai; Slanina, Zdeněk; Univ Arizona, Dept Chem & Biochem (PERGAMON-ELSEVIER SCIENCE LTD, 2018-10)
      In this work, we report a series of defective carbon catalysts prepared through a facile and scalable "-Ndoping-removal" process using seaweed biomass sodium alginate (SA) as precursor. Our systematic studies reveal that the defect content, porosity characteristic and conductivity of defective carbons can be finely tuned by manipulating the pyrolysis temperature and viscosity of precursor polymer SA, which significantly affect the ORR performance. The optimized defective porous carbon catalyst (i.e., D-PC-1( 900)) that was revealed to possess abundant ORR-active defects, large surface area of 1377 m(2)g(-1), abundant hierarchical porosity and good conductivity, exhibited very nice ORR activity and selectivity in 0.1M KOH, comparable to the commercial Pt/C catalyst. In 0.5MH(2)SO(4), considerable ORR activity was also observed for D-PC-1(900), which is among the highest reported for defective carbons and comparable to many of N-doped carbons. Density functional theory calculations indicate that the carbon defect can create the active sites for ORR in acidic media. More importantly, in both alkaline and acidic media, D-PC-1(900) shows much better stability and methanol tolerance than those of the Pt/C catalyst. All these results demonstrate that the seaweed biomass derived defective carbon is an excellent candidate for non-precious-metal ORR catalyst in various fuel cells. (c) 2018 Elsevier Ltd. All rights reserved.
    • Revisiting the Utility of Retrospective Pre-Post Designs: The Need for Mixed-Method Pilot Data

      Geldhof, G. John; Warner, Danielle A.; Finders, Jennifer K.; Thogmartin, Asia A.; Clark, Adam M.; Longway, Kelly A.; Oregon State University; The University of Arizona (Elsevier, 2018-10)
      The retrospective pre-post design affords many benefits to program staff and, accordingly, has piqued renewed interest among applied program evaluators. In particular, the field has witnessed increasing application of a post-program-only data collection strategy in which only posttest and retrospective pretest data are collected. A post-program-only assessment strategy takes considerably less time than is required for collecting pre-program data and presumably has the added benefit of eliminating the impact of response-shift bias. Response-shift bias occurs when the knowledge, skills, or experiences participants gain through program participation leads them to interpret questionnaire items in a qualitatively different manner at pretest versus posttest. In this article, we discuss the strengths and weaknesses associated with administering retrospective pretest assessments and underscore the importance of thoroughly evaluating any application of a retrospective measurement strategy prior to its broader implementation. We provide a practical illustration of this evaluation process using a mixed-method study that assesses one measure of parenting education program effectiveness—the Parenting Skills Ladder.
    • Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control

      Goebel, Sean B.; Guyon, Olivier; Hall, Donald N. B.; Jovanovic, Nemanja; Lozi, Julien; Martinache, Frantz; Univ Arizona, Steward Observ; Univ Arizona, Coll Opt Sci (IOP PUBLISHING LTD, 2018-10)
      Although extreme adaptive optics (ExAO) systems can greatly reduce the effects of atmospheric turbulence and deliver diffraction-limited images, our ability to observe faint objects such as extrasolar planets or debris disks at small angular separations is greatly limited by the presence of a speckle halo caused by imperfect wavefront corrections. These speckles change with a variety of timescales, from milliseconds to many hours, and various techniques have been developed to mitigate them during observations and during data reduction. Detection limits improve with increased speckle reduction, so an understanding of how speckles evolve (particularly at near-infrared wavelengths, which is where most adaptive optics science instruments operate) is of distinct interest. We used a SAPHIRA detector behind Subaru Telescope's SCExAO instrument to collect H-band images of the ExAO-corrected point-spread function (PSF) at a frame rate of 1.68 kHz. We analyzed these images using two techniques to measure the timescales over which the speckles evolved. In the first technique, we analyzed the images in a manner applicable to predicting performance of real-time speckle-nulling loops. We repeated this analysis using data from several nights to account for varying weather and AO conditions. In our second analysis, which follows the techniques employed by Milli et al. (2016) but using data with three orders of magnitude better temporal resolution, we identified a new regime of speckle behavior that occurs at timescales of milliseconds. It is not purely an instrument effect and likely is an atmospheric timescale filtered by the ExAO response. We also observed an exponential decay in the Pearson's correlation coefficients (which we employed to quantify the change in speckles) on timescales of seconds and a linear decay on timescales of minutes, which is in agreement with the behavior observed by Milli et al. For both of our analyses, we also collected similar data sets using SCExAO's internal light source to separate atmospheric effects from instrumental effects.
    • A comparison of the R_h=ct and LCDM cosmologies using the Cosmic Distance Duality Relation

      Melia, Fulvio; Univ Arizona, Dept Phys, Program Appl Math; Univ Arizona, Dept Astron (OXFORD UNIV PRESS, 2018-09-21)
      The cosmic distance duality (CDD) relation (based on the Etherington reciprocity theorem) plays a crucial role in a wide assortment of cosmological measurements. Attempts at confirming it observationally have met with mixed results, though the general consensus appears to be that the data do support its existence in nature. A common limitation with past approaches has been their reliance on a specific cosmological model, or on measurements of the luminosity distance to Type Ia SNe, which introduces a dependence on the presumed cosmology in spite of beliefs to the contrary. Confirming that the CDD is actually realized in nature is crucial because its violation would require exotic new physics. In this paper, we study the CDD using the observed angular size of compact quasar cores and a Gaussian Process reconstruction of the H II galaxy Hubble diagram – without pre-assuming any particular background cosmology. In so doing, we confirm at a very high level of confidence that the angular-diameter and luminosity distances do indeed satisfy the CDD. We then demonstrate the potential power of this result by utilizing it in a comparative test of two competing cosmological models – the Rh = ct universe and ΛCDM – and show that Rh = ct is favoured by the CDD data with a likelihood ∼82.3 per cent compared with ∼17.7 per cent for the standard model.
    • Transforming Growth Factor Beta Signaling in Dendritic Cells Is Required for Immunotolerance to Sperm in the Epididymis

      Pierucci-Alves, Fernando; Midura-Kiela, Monica T.; Fleming, Sherry D.; Schultz, Bruce D.; Kiela, Pawel R.; Univ Arizona, Dept Pediat; Univ Arizona, Dept Immunobiol (FRONTIERS MEDIA SA, 2018-09-16)
      The epididymis exhibits a less restrictive physical blood-tissue barrier than the testis and, while numerous immunosuppressive factors have been identified in the latter, no mechanisms for epididymal immunotolerance have been identified to date. Therefore, data are currently insufficient to explain how the immune system tolerates the extremely large load of novel antigens expressed on sperm, which become present in the male body after puberty, i.e., long after central tolerance was established. This study tested the hypothesis that transforming growth factor beta (TGF beta) signaling in dendritic cells (DCs) is required for immunotolerance to sperm located in the epididymis, and that male mice lacking TGF beta signaling in DCs would develop severe epididymal inflammation. To test this, we employed adult Tgfbr2(Delta DC) males, which exhibit a significant reduction of Tgfbr2 expression and TGF beta signaling in DCs, as reported previously. Results show that Tgfbr2(Delta DC) males exhibit sperm-specific immune response and severe epididymal leukocytosis. This phenotype is consistent with epididymal loss of immunotolerance to sperm and suggests that TGF beta signaling in DCs is a factor required for a non-inflammatory steady state in the epididymis, and therefore for male tract homeostasis and function.
    • Ocean tidal heating in icy satellites with solid shells

      Matsuyama, Isamu; Beuthe, Mikael; Hay, Hamish C.F.C.; Nimmo, Francis; Kamata, Shunichi; Univ Arizona, Lunar & Planetary Lab (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2018-09-15)
      As a long-term energy source, tidal heating in subsurface oceans of icy satellites can influence their thermal, rotational, and orbital evolution, and the sustainability of oceans. We present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness. The stabilizing effect of an overlying shell damps ocean tides, reducing tidal heating. This effect is more pronounced on Enceladus than on Europa because the effective rigidity on a small body like Enceladus is larger. For the range of likely shell and ocean thicknesses of Enceladus and Europa, the thin shell approximation of Beuthe (2016) is generally accurate to less than about 4%. Explaining Enceladus' endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints. The time-averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell, with higher dissipation near the equator and poles for eccentricity and obliquity forcing, respectively. This can lead to unique horizontal shell thickness variations if the shell is conductive. The surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response. For Europa and Enceladus, eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values. Despite the small obliquity values, obliquity forcing generally produces larger phase lags due to the generation of Rossby-Haurwitz waves. If Europa's shell and ocean are, respectively, 10 and 100 km thick, the tide amplitude and phase lag are 26.5 m and <1 degrees for eccentricity forcing, and <2.5 m and <18 degrees for obliquity forcing. Measurement of the obliquity phase lag (e.g. by Europa Clipper) would provide a probe of ocean thickness (C) 2018 Elsevier Inc. All rights reserved.
    • Debiased orbit and absolute-magnitude distributions for near-Earth objects

      Granvik, Mikael; Morbidelli, Alessandro; Jedicke, Robert; Bolin, Bryce; Bottke, William F.; Beshore, Edward; Vokrouhlický, David; Nesvorný, David; Michel, Patrick; Univ Arizona (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2018-09-15)
      The debiased absolute-magnitude and orbit distributions as well as source regions for near-Earth objects (NEOs) provide a fundamental frame of reference for studies of individual NEOs and more complex population-level questions. We present a new four-dimensional model of the NEO population that describes debiased steady-state distributions of semimajor axis, eccentricity, inclination, and absolute magnitude H in the range 17 < H < 25. The modeling approach improves upon the methodology originally developed by Bottke et al. (2000, Science 288, 2190-2194) in that it is, for example, based on more realistic orbit distributions and uses source-specific absolute-magnitude distributions that allow for a power-law slope that varies with H. We divide the main asteroid belt into six different entrance routes or regions (ER) to the NEO region: the v(6), 3:1J, 5:2J and 2:1J resonance complexes as well as Hungarias and Phocaeas. In addition we include the Jupiter-family comets as the primary cometary source of NEOs. We calibrate the model against NEO detections by Catalina Sky Surveys' stations 703 and G96 during 2005-2012, and utilize the complementary nature of these two systems to quantify the systematic uncertainties associated to the resulting model. We find that the (fitted) H distributions have significant differences, although most of them show a minimum power-law slope at H similar to 20. As a consequence of the differences between the ER-specific H distributions we find significant variations in, for example, the NEO orbit distribution, average lifetime, and the relative contribution of different ERs as a function of H. The most important ERs are the v(6) and 3:1J resonance complexes with JFCs contributing a few percent of NEOs on average. A significant contribution from the Hungaria group leads to notable changes compared to the predictions by Bottke et al. in, for example, the orbit distribution and average lifetime of NEOs. We predict that there are 962(-56)(+52) (802(-42)(+48) x 10(3)) NEOs with H < 17.75 (H < 25) and these numbers are in agreement with the most recent estimates found in the literature (the uncertainty estimates only account for the random component). Based on our model we find that relative shares between different NEO groups (Amor, Apollo, Aten, Atira, Vatira) are (39.4,54.4,3.5,1.2,0.3)%, respectively, for the considered H range and that these ratios have a negligible dependence on H. Finally, we find an agreement between our estimate for the rate of Earth impacts by NEOs and recent estimates in the literature, but there remains a potentially significant discrepancy in the frequency of Tunguska-sized and Chelyabinsk-sized impacts. (C) 2018 The Authors. Published by Elsevier Inc.
    • HMGB1 binds to the KRAS promoter G-quadruplex: a new player in oncogene transcriptional regulation?

      Amato, Jussara; Madanayake, Thushara W.; Iaccarino, Nunzia; Novellino, Ettore; Randazzo, Antonio; Hurley, Laurence H.; Pagano, Bruno; Univ Arizona, Coll Pharm (ROYAL SOC CHEMISTRY, 2018-09-04)
      This communication reports on a possible distinct role of HMGB1 protein. Biophysical studies revealed that HMGB1 binds and stabilizes the G-quadruplex of the KRAS promoter element that is responsible for most of the transcriptional activity. Biological data showed that inhibition of HMGB1 increases KRAS expression. These results suggest that HMGB1 could play a role in the gene transcriptional regulation via the functional recognition of the G-quadruplex.
    • Model selection based on the angular-diameter distance to the compact structure in radio quasars

      Melia, F.; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (IOP PUBLISHING LTD, 2018-09-03)
      Of all the distance arid temporal measures in cosmology, the angular-diameter distance, d(A)(z), uniquely reaches a maximum value at some finite redshift z(max )and then decreases to zero towards the Big Bang. This effect has been difficult to observe due to a lack of reliable, standard rulers, though refinements to the identification of the compact structure in radio quasars may have overcome this deficiency. In this letter, we assemble a catalog of 140 such sources with 0 less than or similar to z less than or similar to 3 for model selection and the measurement of z(max). In flat Lambda CDM, we find that Omega(m) = 0.24(-0.09)(+0.1) fully consistent with the Planck optimized value, with z(max) = 1.69. Both of these values are associated with a d(A)(z) indistinguishable from that predicted by the zero active mass condition, rho + 3p = 0, in terms of the total pressure rho and total energy density rho of the cosmic fluid. An expansion driven by this constraint, known as the Rh = ct universe, has z(max )= 1.718, which differs from the Lambda CDM optimized value by less than similar to 1.6%. Indeed, the Bayes Information Criterion favours R-h = ct over flat Lambda CDM with a likelihood of similar to 81% vs. 19%, suggesting that the optimized parameters in Planck Lambda CDM mimic the constraint p = -rho/3.
    • Profiling caregivers: Hormonal variation underlying allomaternal care in wild red-bellied lemurs, Eulemur rubriventer

      Tecot, Stacey R.; Baden, Andrea L.; Univ Arizona, Sch Anthropol; Univ Arizona, Laboratory for the Evolutionary Endocrinology of Primates (Elsevier, 2018-09-01)
    • Profiling caregivers: Hormonal variation underlying allomaternal care in wild red-bellied lemurs, Eulemur rubriventer

      Tecot, Stacey R.; Baden, Andrea L.; Univ Arizona, Sch Anthropol; Univ Arizona, Lab Evolutionary Endocrinol Primates (PERGAMON-ELSEVIER SCIENCE LTD, 2018-09-01)
      Neuroendocrine evidence suggests that paternal care is mediated by hormonal mechanisms, where hormonal changes in expectant and new fathers facilitate infant care. In species with obligate and extensive paternal care such as humans, androgen levels decline once males are paired and have offspring, and in direct response to offspring care. Facultative infant care is widespread in the Order Primates, but the underlying hormonal mechanisms are largely unknown. We found that wild, red-bellied lemurs living in family groups (two adults and their presumed offspring) varied in the amount of care they provided infants. The more fathers invested in helping infants (measured as a composite of carrying, holding, huddling, grooming, and playing), and specifically the more they huddled and groomed with infants, the higher their fecal androgen (fA) levels, contrary to expectations. Carrying was negatively related to fA levels. Helping by subadults and juveniles was not related to their own fA levels. Elevated fA levels during infant dependence have been observed in other vertebrate species, and are thought to reflect reinvestment in mating rather than investment in dependent offspring. However, red-bellied lemurs do not mate until after infants are weaned, and they have long-term pair-bonds, suggesting that elevated fA levels play a role in offspring care. These results support a growing body of research suggesting that elevated androgen levels do not inhibit protective infant care.
    • Half-Watt Tm3+-Doped Fluoride Fiber Laser at 785 nm

      Mollaee, Masoud; Zhu, Xiushan; Zong, Jie; Wiersma, Kort; Chavez-Pirson, Arturo; Norwood, R. A.; Peyghambarian, N.; Univ Arizona, Coll Opt Sci (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018-09-01)
      All-fiber single-transverse-mode laser oscillators operating at 785 nm were demonstrated by splicing a 0.1 mol% Tm3+-doped fluoride fiber with a core diameter of 4 mu m and a numerical aperture of 0.07 to a pair of silica fiber Bragg gratings. About 500 mW of continuous-wave single transverse mode laser output at 784.5 nm with a 3-dB spectral bandwidth of 0.2 nm was obtained by upconversion pumping a 3-m-long gain fiber at 1125 nm. Our experiments show that the ground-state absorption of Tm3(+ )at 785 nm is the origin of low efficiency in previous reports. The efficiency of this all-fiber laser can be improved by using a gain fiber with an optimized overlap between the laser, the pump, and the fiber core, and employing new pumping schemes that deplete the ground state sufficiently.
    • Principal Component Analysis as a Tool for Characterizing Black Hole Images and Variability

      Medeiros, Lia; Lauer, Tod R.; Psaltis, Dimitrios; Özel, Feryal; Univ Arizona, Steward Observ; Univ Arizona, Dept Astron (IOP PUBLISHING LTD, 2018-09-01)
      We explore the use of principal component analysis (PCA) to characterize high-fidelity simulations and interferometric observations of the millimeter emission that originates near the horizons of accreting black holes. We show mathematically that the Fourier transforms of eigenimages derived from PCA applied to an ensemble of images in the spatial domain are identical to the eigenvectors of PCA applied to the ensemble of the Fourier transforms of the images, which suggests that this approach may be applied to modeling the sparse interferometric Fourier-visibilities produced by an array such as the Event Horizon Telescope. We also show that the simulations in the spatial domain can themselves be compactly represented with a PCA-derived basis of eigenimages, which allows for detailed comparisons to be made between variable observations and time-dependent models, as well as for detection of outliers or rare events within a time series of images. Furthermore, we demonstrate that the spectrum of PCA eigenvalues is a diagnostic of the power spectrum of the structure and, hence, of the underlying physical processes in the simulated and observed images.
    • A lattice QCD study of pion-nucleon scattering in the Roper channel

      Leskovec, Luka; Lang, Christian, B; Padmanath, M.; Prelovsek, Sasa; University of Graz; Regensburg University; University of Ljubljana; Univ Arizona, Dept Phys, Tucson, AZ 85721 USA (SPRINGER WIEN, 2018-09)
      We present a lattice QCD study of the puzzling positive-parity nucleon channel, where the Roper resonance N∗(1440) resides in experiment. The study is based on an ensemble of gauge configurations with Nf=2+1 Wilson-clover fermions with a pion mass of 156 MeV and lattice size L=2.9 fm. We use several qqq interpolating fields combined with Nπ and Nσ two-hadron operators in calculating the energy spectrum in the rest frame. Combining experimental Nπ phase shifts with elastic approximation and the Lüscher formalism suggests in the spectrum an additional energy level near the Roper mass mR=1.43 GeV for our lattice. We do not observe any such additional energy level, which implies that Nπ elastic scattering alone does not render a low-lying Roper resonance. The current status indicates that the N∗(1440) might arise as dynamically generated resonance from coupling to other channels, most notably the Nππ .
    • Antiwindup Terminal Sliding Mode Control for Mars Entry Using Supertwisting Sliding Mode Disturbance Observer

      Jiang, Xiuqiang; Li, Shuang (AMER SOC CIVIL ENGINEERS, 2018-09)
      Uncertainty and external disturbance during the Mars entry process inevitably degrade the performance of Mars entry guidance and control algorithms. Traditional approaches focus on suppressing disturbances and compensating uncertainties, which usually results in larger control responses beyond the limited control capability of a Mars entry vehicle. This paper further takes the limited actuator ability into consideration and proposes the Mars entry robust attitude control strategy using the terminal sliding mode control (TSMC) with antiwindup (AW) and a supertwisting sliding mode disturbance observer (SMDO). First, terminal sliding mode control with antiwindup is developed to robustly track the nominal attitude command under uncertainty and limited control capability. Then, the supertwisting sliding mode disturbance observer is introduced to online estimate the disturbances and further enhance the attitude control accuracy and robustness. Finally, the comparison simulation results illustrate that the proposed control strategy not only performs well in tracking the reference commands even in the presence of uncertain disturbance, but also avoids the control saturation issue.
    • Clinical learning experiences of nursing students using an innovative clinical partnership model: A non-randomized controlled trial

      Chan, Aileen W.K.; Tang, Fiona W.K.; Choi, Kai Chow; Liu, Ting; Taylor-Piliae, Ruth E.; Univ Arizona, Coll Nursing (CHURCHILL LIVINGSTONE, 2018-09)
      Background: Clinical practicum is a major learning component for pre-registration nursing students. Various clinical practicum models have been used to facilitate students' clinical learning experiences, employing both university-based and hospital-based clinical teachers. Considering the strengths and limitations of these clinical practicum models, along with nursing workforce shortages, we developed and tested an innovative clinical partnership model (CPM) in Hong Kong. Objective: To evaluate an innovative CPM among nursing students actual and preferred clinical learning environment, compared with a conventional facilitation model (CFM). Design: A non-randomized controlled trial examining students' clinical experiences, comparing the CPM (supervised by hospital clinical teacher) with the CFM (supervised by university clinical teacher). Setting One university in Hong Kong. Participants: Pre-registration nursing students (N = 331), including bachelor of nursing (n = 246 year three-BN) and masters-entry nursing (n = 85 year one-MNSP). Methods: Students were assigned to either the CPM (n = 48 BN plus n = 85 MNSP students) or the CFM (n = 198 BN students) for their clinical practice experiences in an acute medical-surgical ward. Clinical teachers supervised between 6 and 8 students at a time, during these clinical practicums (duration = 4-6 weeks). At the end of the clinical practicum, students were invited to complete the Clinical Learning Environment Inventory (CLEI). Analysis of covariance was used to compare groups; adjusted for age, gender and prior work experience. Results: A total of 259 students (mean age = 22 years, 76% female, 81% prior work experience) completed the CLEI (78% response rate). Students had higher scores on preferred versus actual experiences, in all domains of the CLEI. CPM student experiences indicated a higher preferred task orientation (p = 0.004), while CFM student experiences indicated a higher actual (p < 0.001) and preferred individualization (p = 0.005). No significant differences were noted in the other domains. Conclusions: The CPM draws on the strengths of existing clinical learning models and provides complementary methods to facilitate clinical learning for pre-registration nursing students. Additional studies examining this CPM with longer duration of clinical practicum are recommended.