The Blurred Line between “Long” and “Short”: How the Length of Video Lectures Affects the Viewing Behavior of E-Learners

Recent research has focused on the impact of video lectures on students’ academic performance rather than the viewing behavior of learners. In this study, we investigate the learners’ preferences of video lectures in terms of the length as well as the devices used to access the online learning material. We published two versions of video lectures on two YouTube channels. The online material was produced by recording a real face-to-face class context at the Arab Open University. The video recorded material belongs to a first level course offered to students at the Faculty of Computer Studies. The first version of the online lectures comprised 7 videos and is, hence, called long-run version. The second version, termed as short-run version, consisted of 28 video lectures. Video contents are identical in both versions. Total recording time amounted to 528 minutes in both video versions with an average of 75 and 19 minutes in long-run and short-run versions, respectively. We found that though students alternated between the use of mobile phones, tablets and desktops, however, they mainly accessed the online material through desktops. Moreover, students spent a total of 43765 minutes in viewing the long-run videos compared with 4766 minutes spent on the short-run ones. Considering the number of views (3143 for the long-run and 846 views for the short-run videos) yields average viewing times of 13.92 and 5.63 minutes per views for the long-run and short-run videos, respectively. This is interesting, for these results show that students are willing to spend approximately 14 minutes when viewing an approximately 75 minutes long video lecture, but when offered a 22 minutes long alternative, the time they spend in viewing does not exceed 6 minutes on average. Our results imply that students do access the online video lectures for learning purposes. However, more should be done, so as to approach near-optimal lengths of video lectures that facilitate a complete viewing of the learning material. Keywords: Video lectures, Blended learning, Viewing behavior, Big data analysi

Feedback regulation of the heat shock response in E. coli

Survival of organisms in extreme conditions has necessitated the evolution of stress response networks that detect and respond to environmental changes. Among the extreme conditions that cells must face is the exposure to higher than normal temperatures. In this paper, we propose a detailed biochemical model that captures the dynamical nature of the heat-shock response in Escherichia coli. Using this model, we show that both feedback and feedforward control are utilized to achieve robustness, performance, and efficiency of the response to the heat stress. We discuss the evolutionary advantages that feedback confers to the system, as compared to other strategies that could have been implemented to get the same performance

Assignment of PCR markers to river buffalo chromosomes

International audienc

NATURAL ENEMIES ASSOCIATED WITH MEALY PLUM APHID HYALOPTERUS PRUNI (Geoff.), (HOMOPTERA: APHIDIDAE) INFESTED APRICOT TREES, AT QALUBIA GOVERNORATE

The present work was carried out to study the population dynamics of the mealy plum aphid Hyalopterus pruni (Geoff.) and related parasitoids and predators on apricot trees, during the two successive seasons, 2003 and 2004, at Qalubia Gover-norate. The obtained data revealed that, the occurrence of H. pruni on apricot trees covered 5 months (from February to June). The mean total numbers of this aphid species per season were 1.78 (0.01-6.37) and 2.83 (0.00-10.01) individuals./leaf. The maximum numbers of H. pruni were recorded during the 2nd weeks of April, 2003 and 2004. No aphid individuals were observed during the period extended from July to September, in the two studied seasons. Four species of parasitoids; namely Aphidius matricariae Hal., Lysiphylbus sp. (1ry parasitoids) and 2 species of Alloxysta spp. (2ry parasitoids) were recorded during this study, attacking H. pruni. These parasitoid species were found during nearly three months of each season, in connection with the population density of the previous aphid species. The first para-sitoid was the highest in its numbers. The total numbers of predatory species per season were 407 and 1082 individuals, in the two studied seasons, 2003 and 2004, respectively. The maximum monthly occurrence of these predatory species was dur-ing April, 2003 (146 individuals) and April, 2004 (581 individuals), respectively. The predator Chrysoperla septempunctata L. had the highest percentages of occur-rence among other recorded predatory species (52.83 and 73.01%, respectively). In general, the parasitoid A. matricariae and the predator C. septempunctata, could be mass reared and released for controlling H. pruni on apricot trees with other availa-ble safe control methods developed in Integrated Pest Management (IPM) programs against this pest

A review of compressors for high temperature heat pumps

Data availability: No data was used for the research described in the article.The development of high temperature heat pumps for waste heat recovery benefits industrial processes by meeting demand, increasing energy efficiency, and reducing emissions. The aim of such systems is to upgrade waste heat streams, typically around 50 °C to 100 °C, to higher temperatures ranging from 100 °C to around 200 °C. A primary challenge in getting the required high temperatures is the compression system. There is a plethora of recently published research papers including reviews that address high temperature heat pumps. However, there has been no comprehensive review addressing compression systems, despite their major influence in the successful development of high temperature heat pumps; this paper provides a comprehensive review of such compressors. Firstly, an overview of heat pump systems is provided, which covers cycle arrangements and working fluid selection. This is followed by a review of the different compressor technologies used, and the development of relevant modelling and design tools. Finally, suggestions for future directions in research for high temperature heat pump compressors are provided. It was found that screw compressors have been the obvious choice for heat pumps due to the experience gained from the refrigeration industry. However, the temperatures they can handle are constrained by the maximum possible limitation to avoid oil degradation. For higher temperatures, better efficiency, and larger capacity, it seems that the alternative is turbo-compressors. Nevertheless, there is a lack of experience in this area and more research and development efforts are required to enable these machines to achieve their potential in high temperature heat pumps

On the Production of π+π+\pi^+\pi^+ Pairs in pp Collisions at 0.8 GeV

Data accumulated recently for the exclusive measurement of the $pp\to pp\pi^+\pi^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp \to nn\pi^+\pi^+$ reaction channel. The latter is expected to be the only $\pi\pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $\pi\pi$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp \to nn \pi^+\pi^+$ reaction. This gives an upper limit for the cross section of 0.16 $\mu$b (90% C.L.), which is more than an order of magnitude smaller than the cross sections of the other two-pion production channels at the same incident energy

A review of compressors for high temperature heat pumps

The development of high temperature heat pumps for waste heat recovery benefits industrial processes by meeting demand, increasing energy efficiency, and reducing emissions. The aim of such systems is to upgrade waste heat streams, typically around 50 °C to 100 °C, to higher temperatures ranging from 100 °C to around 200 °C. A primary challenge in getting the required high temperatures is the compression system. There is a plethora of recently published research papers including reviews that address high temperature heat pumps. However, there has been no comprehensive review addressing compression systems, despite their major influence in the successful development of high temperature heat pumps; this paper provides a comprehensive review of such compressors. Firstly, an overview of heat pump systems is provided, which covers cycle arrangements and working fluid selection. This is followed by a review of the different compressor technologies used, and the development of relevant modelling and design tools. Finally, suggestions for future directions in research for high temperature heat pump compressors are provided. It was found that screw compressors have been the obvious choice for heat pumps due to the experience gained from the refrigeration industry. However, the temperatures they can handle are constrained by the maximum possible limitation to avoid oil degradation. For higher temperatures, better efficiency, and larger capacity, it seems that the alternative is turbo-compressors. Nevertheless, there is a lack of experience in this area and more research and development efforts are required to enable these machines to achieve their potential in high temperature heat pumps

De novo design of bioactive protein switches.

Allosteric regulation of protein function is widespread in biology, but is challenging for de novo protein design as it requires the explicit design of multiple states with comparable free energies. Here we explore the possibility of designing switchable protein systems de novo, through the modulation of competing inter- and intramolecular interactions. We design a static, five-helix 'cage' with a single interface that can interact either intramolecularly with a terminal 'latch' helix or intermolecularly with a peptide 'key'. Encoded on the latch are functional motifs for binding, degradation or nuclear export that function only when the key displaces the latch from the cage. We describe orthogonal cage-key systems that function in vitro, in yeast and in mammalian cells with up to 40-fold activation of function by key. The ability to design switchable protein functions that are controlled by induced conformational change is a milestone for de novo protein design, and opens up new avenues for synthetic biology and cell engineering

On the SigmaN cusp in the pp -> pK+Lambda reaction

Measurements of the $pp \to pK^+\Lambda$ reaction at $T_p$ = 2.28 GeV have been carried out at COSY-TOF. In addition to the $\Lambda p$ FSI and $N^*$ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the $p\Lambda$-invariant mass. The structure appears at the $pp \to$N$K^+\Sigma$ threshold and is interpreted as $\Sigma$N cusp effect. The observed width of 20 MeV/$c^2$ is substantially broader than anticipated from previous inclusive measurements. Angular distributions of this cusp structure are shown to be dissimilar to those in the residual $pK^+\Lambda$ channel, but similar to those observed in the $pK^+\Sigma^0$ channel

Cross section of the pp→K+Σ+npp\to K^+\Sigma^+n reaction close to threshold

We have measured inclusive data on $K^+$-meson production in $pp$ collisions at COSY J\"ulich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: $\Lambda p$, $\Sigma^0p$ and $\Sigma^+n$. The cross section for the $\Sigma^+n$ channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.Comment: accepted by Phys. lett. B some typos correcte