Social effects of collaborative learning in primary schools

There is conflicting evidence on whether collaborative group work leads to improved classroom relations, and if so how. A before and after design was used to measure the impact on work and play relations of a collaborative learning programme involving 575 students 9e12 years old in single- and mixed-age classes across urban and rural schools. Data were also collected on student interactions and teacher ratings of their group-work skills. Analysis of variance revealed significant gains for both types of relation. Multilevel modelling indicated that better work relations were the product of improving group skills, which offset tensions produced by transactive dialogue, and this effect fed through in turn to play relations. Although before intervention rural children were familiar with each other neither this nor age mix affected outcomes. The results suggest the social benefits of collaborative learning are a separate outcome of group work, rather than being either a pre-condition for, or a direct consequence of successful activity, but that initial training in group skills may serve to enhance these benefits.

A low-cost solution for the restoration of femoral head centre during total hip arthroplasty

Restoration of joint centre during total hip arthroplasty is critical. While computer-aided navigation can improve accuracy during total hip arthroplasty, its expense makes it inaccessible to the majority of surgeons. This article evaluates the use, in the laboratory, of a calliper with a simple computer application to measure changes in femoral head centres during total hip arthroplasty. The computer application was designed using Microsoft Excel and used calliper measurements taken pre- and post-femoral head resection to predict the change in head centre in terms of offset and vertical height between the femoral head and newly inserted prosthesis. Its accuracy was assessed using a coordinate measuring machine to compare changes in preoperative and post-operative head centre when simulating stem insertion on 10 sawbone femurs. A femoral stem with a modular neck was used, which meant nine possible head centre configurations were available for each femur, giving 90 results. The results show that using this technique during a simulated total hip arthroplasty, it was possible to restore femoral head centre to within 6?mm for offset (mean 1.67?±?1.16?mm) and vertical height (mean 2.14?±?1.51?mm). It is intended that this low-cost technique be extended to inform the surgeon of a best-fit solution in terms of neck length and neck type for a specific prosthesis.

Conjugate heat transfer and film cooling of a multi-stage cooling scheme

Cooling techniques play a key role in improving efficiency and power output of modern gas turbines. The conjugate technique of film and impingement cooling schemes is considered in this study. The Multi-Stage Cooling Scheme (MSCS) involves coolant passing from inside to outside turbine blade through two stages. The first stage; the coolant passes through first hole to internal gap where the impinging jet cools the external layer of the blade. Finally, the coolant passes through the internal gap to the second hole which has specific designed geometry for external film cooling. The effect of design parameters, such as, offset distance between two-stage holes, gap height, and inclination angle of the first hole, on upstream conjugate heat transfer rate and downstream film cooling effectiveness performance are investigated computationally. An Inconel 617 alloy with variable properties is selected for the solid material. The conjugate heat transfer and film cooling characteristics of MSCS are analyzed across blowing ratios of Br = 1 and 2 for density ratio, 2. This study presents upstream wall temperature distributions due to conjugate heat transfer for different gap design parameters. The maximum film cooling effectiveness with upstream conjugate heat transfer is less than adiabatic film cooling effectiveness by 24–34%. However, the full coverage of cooling effectiveness in spanwise direction can be obtained using internal cooling with conjugate heat transfer, whereas adiabatic film cooling effectiveness has narrow distribution.

Rapid rise in Effective Sea-Level in southwest Bangladesh: Its causes and contemporary rates

Evidence is presented from three estuarine tide gauges located in the
Sundarban area of southwest Bangladesh of relative sea level rise
substantially in excess of the generally accepted rates from altimetry, as
well as previous tide-gauge analyses. It is proposed that the difference
arises from the use of relative mean sea level (RMSL) to characterise the
present and future coastal flood hazard, since RMSL can be misleading in
estuaries in which tidal range is changing. Three tide gauges, one located in
the uninhabited mangrove forested area (Sundarban) of southwest
Bangladesh, the others in the densely populated polder zone north of the
present Sundarban, show rates of increase in RMSL ranging from 2.8 mm
a-1 to 8.8 mm a-1. However, these trends in RMSL disguise the fact that high
water levels in the polder zone have been increasing at an average rate of
15.9 mm a-1 and a maximum of 17.2 mm a-1. In an area experiencing tidal
range amplification, RMSL will always underestimate the rise in high water
levels; consequently, as an alternative to RMSL, the use of trends in high
water maxima or ‘Effective Sea Level Rise’ (ESLR) is adopted as a more
strategic parameter to characterise the flooding hazard potential. The rate
of increase in ESLR is shown to be due to a combination of deltaic
subsidence, including sediment compaction, and eustatic sea level rise, but
principally as a result of increased tidal range in estuary channels recently
constricted by embankments. These increases in ESLR have been partially
offset by decreases in fresh water discharge in those estuaries connected
to the Ganges. The recognition of increases of the effective sea level in the
Bangladesh Sundarban, which are substantially greater than increases in
mean sea level, is of the utmost importance to flood management in this
low-lying and densely populated area.

On the progenitor of the type IIP SN 2013ej in M74

We use natural seeing imaging of SN 2013ej in M74 to identify a progenitor candidate in archival Hubble Space Telescope (HST) + Advanced Camera for Survey images. We find a source coincident with the supernova (SN) in the F814W filter within the total 75 mas (~3 pc astrometric uncertainty; however, the position of the progenitor candidate in contemporaneous F435W and F555W filters is significantly offset. We conclude that the 'progenitor candidate' is in fact two physically unrelated sources; a blue source which is likely unrelated to the SN, and a red source which we suggest exploded as SN 2013ej. Deep images with the same instrument on board HST taken when the SN has faded (in approximately two year's time) will allow us to accurately characterize the unrelated neighbouring source and hence determine the intrinsic flux of the progenitor in three filters.We suggest that the F814W flux is dominated by the progenitor of SN 2013ej, and assuming a bolometric correction appropriate to an M-type supergiant, we estimate that the mass of the progenitor of SN 2013ej was between 8 and 15.5M⊙. 

Ages of 24 widespread tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of the timing and palaeoclimatic implications of the Lateglacial cool episode recorded at Kaipo bog

Tephras are important for the NZ-INTIMATE project because they link all three records comprising the composite inter-regional stratotype developed for the New Zealand climate event stratigraphy (NZ-CES). Here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30,000 calendar (cal.) years ago in New Zealand to help facilitate their use as chronostratigraphic dating tools for the NZ-CES and for other palaeoenvironmental and geological applications. The selected tephras comprise 12 rhyolitic tephras from Taupo, nine rhyolitic tephras from Okataina, one peralkaline rhyolitic tephra from Tuhua, and one andesitic tephra each from Tongariro and Egmont/Taranaki volcanic centres. Age models for the tephras were obtained using three methods: (i) C-based wiggle-match dating of wood from trees killed by volcanic eruptions (these dates published previously); (ii) flexible depositional modelling of a high-resolution C-dated age-depth sequence at Kaipo bog using two Bayesian-based modelling programs, Bacon and OxCal's P_Sequence function, and the IntCal09 data set (with SH offset correction-44±17yr); and (iii) calibration of C ages using OxCal's Tau_Boundary function and the SHCal04 and IntCal09 data sets. Our preferred dates or calibrated ages for the 24 tephras are as follows (youngest to oldest, all mid-point or mean ages of 95% probability ranges): Kaharoa AD 1314±12; Taupo (Unit Y) AD 232±10; Mapara (Unit X) 2059±118cal.yrBP; Whakaipo (Unit V) 2800±60cal.yrBP; Waimihia (Unit S) 3401±108cal.yrBP; Stent (Unit Q) 4322±112cal.yrBP; Unit K 5111±210cal.yrBP; Whakatane 5526±145cal.yrBP; Tuhua 6577±547cal.yrBP; Mamaku 7940±257cal.yrBP; Rotoma 9423±120cal.yrBP; Opepe (Unit E) 9991±160cal.yrBP; Poronui (Unit C) 11,170±115cal.yrBP; Karapiti (Unit B) 11,460±172cal.yrBP; Okupata 11,767±192cal.yrBP; Konini (bed b) 11,880±183cal.yrBP; Waiohau 14,009±155cal.yrBP; Rotorua 15,635±412cal.yrBP; Rerewhakaaitu 17,496±462cal.yrBP; Okareka 21,858±290cal.yrBP; Te Rere 25,171±964cal.yrBP; Kawakawa/Oruanui 25,358±162cal.yrBP; Poihipi 28,446±670cal.yrBP; and Okaia 28,621±1428cal.yrBP.Secondly, we have re-dated the start and end of the Lateglacial cool episode (climate event NZce-3 in theNZ-CES), previously referred to as the Lateglacial climate reversal, as defined at Kaipo bog in eastern North Island, New Zealand, using both Bacon and OxCal P_Sequence modelling with the IntCal09 data set. The ca1200-yr-long cool episode, indicated by a lithostratigraphic change in the Kaipo peat sequence to grey mudwith lowered carbon content, and a high-resolution pollen-derived cooling signal, began 13,739±125cal.yrBP and ended 12,550±140cal.yrBP (mid-point ages of the 95% highest posterior density regions, Bacon modelling). The OxCal modelling, generating almost identical ages, confirmed these ages. The Lateglacial cool episode (ca 13.8-12.6cal.kaBP) thus overlaps a large part of the entire Antarctic Cold Reversal chronozone (ca 14.1-12.4cal.kaBP or ca 14.6-12.8cal.kaBP), and an early part of the Greenland Stadial-1 (Younger Dryas) chronozone (ca 12.9-11.7cal.kaBP). The timing of the Lateglacial cool episode at Kaipo is broadly consistent with the latitudinal patterns in the Antarctic Cold Reversal signal suggested for the New Zealand archipelago from marine and terrestrial records, and with records from southern South America. © 2012 Elsevier Ltd.

Ergodic Capacity of Cognitive TAS/GSC Relaying in Nakagami-m Fading Channels

We examine the impact of transmit antenna selection with receive generalized selection combining (TAS/GSC) for cognitive decode-and-forward (DF) relaying in Nakagami-m fading channels. We select a single transmit antenna at the secondary transmitter which maximizes the receive signal-to-noise ratio (SNR) and combine a subset of receive antennas with the largest SNRs at the secondary receiver. In an effort to assess the performance, we first derive the probability density function and cumulative distribution function of the end-to-end SNR using the moment generating function. We then derive new exact closed-form expression for the ergodic capacity. More importantly, by deriving the asymptotic expression for the high SNR approximation of the ergodic capacity, we gather deep insights into the high SNR slope and the power offset. Our results show that the high SNR slope is 1/2 under the proportional interference power constraint. Under the fixed interference power constraint, the high SNR slope is zero.

On the MIMO Capacity with Residual Transceiver Hardware Impairments

Radio-frequency (RF) impairments in the transceiver hardware of communication systems (e.g., phase noise (PN), high power amplifier (HPA) nonlinearities, or in-phase/quadrature-phase (I/Q) imbalance) can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although calibration algorithms can partially compensate these impairments, the remaining distortion still has substantial impact. Despite this, most prior works have not analyzed this type of distortion. In this paper, we investigate the impact of residual transceiver hardware impairments on the MIMO system performance. In particular, we consider a transceiver impairment model, which has been experimentally validated, and derive analytical ergodic capacity expressions for both exact and high signal-to-noise ratios (SNRs). We demonstrate that the capacity saturates in the high-SNR regime, thereby creating a finite capacity ceiling. We also present a linear approximation for the ergodic capacity in the low-SNR regime, and show that impairments have only a second-order impact on the capacity. Furthermore, we analyze the effect of transceiver impairments on large-scale MIMO systems; interestingly, we prove that if one increases the number of antennas at one side only, the capacity behaves similar to the finite-dimensional case. On the contrary, if the number of antennas on both sides increases with a fixed ratio, the capacity ceiling vanishes; thus, impairments cause only a bounded offset in the capacity compared to the ideal transceiver hardware case.

Technical and allocative efficiency of irrigation water use in the Guanzhong Plain, China

Due to increasing water scarcity, accelerating industrialization and urbanization, efficiency of irrigation water use in Northern China needs urgent improvement. Based on a sample of 347 wheat growers in the Guanzhong Plain, this paper simultaneously estimates a production function, and its corresponding first-order conditions for cost minimization, to analyze efficiency of irrigation water use. The main findings are that average technical, allocative, and overall economic efficiency are 0.35, 0.86 and 0.80, respectively. In a second stage analysis, we find that farmers’ perception of water scarcity, water price and irrigation infrastructure increase irrigation water allocative efficiency, while land fragmentation decreases it. We also show that farmers’ income loss due to higher water prices can be offset by increasing irrigation water use efficiency.

Investigation of the process energy demand in polymer extrusion: a brief review and an experimental study

Extrusion is one of the fundamental production methods in the polymer processing industry and is used in the production of a large number of commodities in a diverse industrial sector. Being an energy intensive production method, process energy efficiency is one of the major concerns and the selection of the most energy efficient processing conditions is a key to reducing operating costs. Usually, extruders consume energy through the drive motor, barrel heaters, cooling fans, cooling water pumps, gear pumps, etc. Typically the drive motor is the largest energy consuming device in an extruder while barrel/die heaters are responsible for the second largest energy demand. This study is focused on investigating the total energy demand of an extrusion plant under various processing conditions while identifying ways to optimise the energy efficiency. Initially, a review was carried out on the monitoring and modelling of the energy consumption in polymer extrusion. Also, the power factor, energy demand and losses of a typical extrusion plant were discussed in detail. The mass throughput, total energy consumption and power factor of an extruder were experimentally observed over different processing conditions and the total extruder energy demand was modelled empirically and also using a commercially available extrusion simulation software. The experimental results show that extruder energy demand is heavily coupled between the machine, material and process parameters. The total power predicted by the simulation software exhibits a lagging offset compared with the experimental measurements. Empirical models are in good agreement with the experimental measurements and hence these can be used in studying process energy behaviour in detail and to identify ways to optimise the process energy efficiency.

Absolute Magnitudes of Pan-STARRS PS1 Asteroids

Absolute magnitude (H) of an asteroid is a fundamental parameter describing the size and the apparent brightness of the body. Because of its surface shape, properties and changing illumination, the brightness changes with the geometry and is described by the phase function governed by the slope parameter (G). Although many years have been spent on detailed observations of individual asteroids to provide H and G, vast majority of minor planets have H based on assumed G and due to the input photometry from multiple sources the errors of these values are unknown. We compute H of ~ 180 000 and G of few thousands asteroids observed with the Pan-STARRS PS1 telescope in well defined photometric systems. The mean photometric error is 0.04 mag. Because on average there are only 7 detections per asteroid in our sample, we employed a Monte Carlo (MC) technique to generate clones simulating all possible rotation periods, amplitudes and colors of detected asteroids. Known asteroid colors were taken from the SDSS database. We used debiased spin and amplitude distributions dependent on size, spectral class distributions of asteroids dependent on semi-major axis and starting values of G from previous works. H and G (G12 respectively) were derived by phase functions by Bowell et al. (1989) and Muinonen et al. (2010). We confirmed that there is a positive systematic offset between H based on PS1 asteroids and Minor Planet Center database up to -0.3 mag peaking at 14. Similar offset was first mentioned in the analysis of SDSS asteroids and was believed to be solved by weighting and normalizing magnitudes by observatory codes. MC shows that there is only a negligible difference between Bowell's and Muinonen's solution of H. However, Muinonen's phase function provides smaller errors on H. We also derived G and G12 for thousands of asteroids. For known spectral classes, slope parameters agree with the previous work in general, however, the standard deviation of G in our sample is twice as larger, most likely due to sparse phase curve sampling. In the near future we plan to complete the H and G determination for all PS1 asteroids (500,000) and publish H and G values online. This work was supported by NASA grant No. NNX12AR65G.

Absolute Magnitudes of Pan-STARRS 1 Asteroids

It is well known that the absolute magnitudes (H) in the MPCORB and ASTORB orbital element catalogs suffer from a systematic offset. Juric at al. (2002) found 0.4 mag offset in the SDSS data and detailed light curve studies of WISE asteroids by Pravec et al. (2012) revealed size-dependent offsets of up to 0.5 mag. The offsets are thought to be caused by systematic errors introduced by earlier surveys using different photometric catalogs and filters. The next generation asteroid surveys provide an order of magnitude more asteroids and well-defined and calibrated magnitudes. The Pan-STARRS 1 telescope (PS1) has observed hundreds of thousands asteroids, submitted more than 2 million detections to the Minor Planet Center (MPC) and discovered almost 300 NEOs since the beginning of operations in late 2010. We transformed the observed apparent magnitudes of PS1-detected asteroids from the gP1,rP1,iP1,yP1,zP1 and wP1-bands into Johnson photometric system by assuming the mean S and C-type asteroid color (Fitzsimmons 2011 - personal communication, Schlafly et al. 2012, Magnier et al. 2012 - in preparation) and calculated the absolute magnitude (H) in the V-band and its uncertainty (Bowell et al., 1989) for more than 200,000 known asteroids having on average 6.7 detections per object. The H error with respect to the MPCORB catalog revealed a mean offset of -0.49+0.30 mag in good agreement with published values. We will also discuss the statistical and systematical errors in H and slope parameter G.

Absolute magnitudes and slope parameters of Pan-STARRS PS1 asteroids -preliminary results

We present the study of absolute magnitude (H) and slope parameter (G) of 170,000 asteroids observed by the Pan-STARRS1 telescope during the period of 15 months within its 3-year all-sky survey mission. The exquisite photometry with photometric errors below 0.04 mag and well-defined filter and photometric system allowed to derive H and G with statistical and systematic errors. Our new approach lies in the Monte Carlo technique simulating rotation periods, amplitudes, and colors, and deriving most-likely H, G and their systematic errors. Comparison of H_M by Muinonen's phase function (Muinonen et al., 2010) with the Minor Planet Center database revealed a negative offset of 0.22±0.29 meaning that Pan-STARRS1 asteroids are fainter. We showed that the absolute magnitude derived by Muinonen's function is systematically larger on average by 0.14±0.29 and by 0.30±0.16 when assuming fixed slope parameter (G=0.15, G_{12}=0.53) than Bowell's absolute magnitude (Bowell et al., 1989). We also derived slope parameters of asteroids of known spectral types and showed a good agreement with the previous studies within the derived uncertainties. However, our systematic errors on G and G_{12} are significantly larger than in previous work, which is caused by poor temporal and phase coverage of vast majority of the detected asteroids. This disadvantage will vanish when full survey data will be available and ongoing extended and enhanced mission will provide new data.

Field test of multiple 1/10 scale tidal turbines in steady flows

Queen's University Belfast and Wave Barrier Ltd have developed a tidal testing platform to test hydrokinetic turbines at medium scale. Multiple turbines can be pushed through still water conditions, in steady-state pushing tests. Experiments were conducted to evaluate the interactions between two identical, mono-strut, horizontal axis tidal turbines (HATTs) of 1.5 m diameter (D) rotor. Their relative performance when located individually, in-plane and in-line are investigated. The data shows a high consistency in the power curves at different flow speeds, which indicates high repeatability in this Reynolds range. For an individual turbine, there is no performance difference when the rotor is mounted either upstream or downstream of the supporting structure. When placed in-plane, the turbines have no adverse effect on one another. When spaced in-line with 2D separation, there is a 63% reduction in the performance of the downstream turbine. At 6D downstream this performance reduction is still 59%, indicating some wake recovery between 2D and 6D, though the influence from the upstream rotor persists to at least 6D downstream of the first device. In contrast the performance of the downstream turbine when placed at 1.5D offset of the upstream device at 6D downstream is approximately recovered to the individual turbine performance.

Secure Transmission in MIMO Wiretap Channels Using General-Order Transmit Antenna Selection with Outdated CSI

In this paper, we propose general-order transmit antenna selection to enhance the secrecy performance of multiple-input–multiple-output multieavesdropper channels with outdated channel state information (CSI) at the transmitter. To evaluate the effect of the outdated CSI on the secure transmission of the system, we investigate the secrecy performance for two practical scenarios, i.e., Scenarios I and II, where the eavesdropper's CSI is not available at the transmitter and is available at the transmitter, respectively. For Scenario I, we derive exact and asymptotic closed-form expressions for the secrecy outage probability in Nakagami- m fading channels. In addition, we also derive the probability of nonzero secrecy capacity and the \varepsilon -outage secrecy capacity, respectively. Simple asymptotic expressions for the secrecy outage probability reveal that the secrecy diversity order is reduced when the CSI is outdated at the transmitter, and it is independent of the number of antennas at each eavesdropper N_text\rm{E} , the fading parameter of the eavesdropper's channel m_text\rm{E} , and the number of eavesdroppers M . For Scenario II, we make a comprehensive analysis of the average secrecy capacity obtained by the system. Specifically, new closed-form expressions for the exact and asymptotic average secrecy capacity are derived, which are valid for general systems with an arbitrary number of antennas, number of eavesdroppers, and fading severity parameters. Resorting to these results, we also determine a high signal-to-noise ratio power offset to explicitly quantify the impact of the main c- annel and the eavesdropper's channel on the average secrecy capacity.