7,049 research outputs found
A Hybrid Approach to Case Teaching
We structure case based teaching using a combination of computer-support technology and in-class activities. We create and design an on-line learning tool, Case Study On-line (CSOL) that enables instructor to structure the delivery of teaching resources and set up assignment tasks in the system. The tool enables tasks to be set in a way that they can be completed sequentially, and learning resources can be accessed only when required by students. Upon submission of their assignments, students can promptly receive instructors explanations to the tasks. Follow up activities take place in class, with the objective to promote active learning. The tool was adopted over two semesters in an undergraduate economics course and surveys were conducted among the students to evaluate the effectiveness of the tool. The results of the survey were very positive, providing support to our belief that a system of well-designed case teaching delivery tool, together with classroom activities, is able to increase the level of students engagement and interest. The paper helps to address some concerns about teaching methods in undergraduate economics courses.Technologies-based Instruction, In-class Activities, Scaffolding, Active-based Learning
The electromagnetic and gravitational-wave radiations of X-ray transient CDF-S XT2
Binary neutron star (NS) mergers may result in remnants of supra-massive or
even stable NS, which have been supported indirectly by observed X-ray plateau
of some gamma-ray bursts (GRBs) afterglow. Recently, Xue et al. (2019)
discovered a X-ray transient CDF-S XT2 that is powered by a magnetar from
merger of double NS via X-ray plateau and following stepper phase. However, the
decay slope after the plateau emission is a little bit larger than the
theoretical value of spin-down in electromagnetic (EM) dominated by losing its
rotation energy. In this paper, we assume that the feature of X-ray emission is
caused by a supra-massive magnetar central engine for surviving thousands of
seconds to collapse black hole. Within this scenario, we present the
comparisons of the X-ray plateau luminosity, break time, and the parameters of
magnetar between CDF-S XT2 and other short GRBs with internal plateau samples.
By adopting the collapse time to constrain the equation of state (EOS), we find
that three EOSs (GM1, DD2, and DDME2) are consistent with the observational
data. On the other hand, if the most released rotation energy of magnetar is
dominated by GW radiation, we also constrain the upper limit of ellipticity of
NS for given EOS, and it is range in . Its GW signal
can not be detected by aLIGO or even for more sensitive Einstein Telescope in
the future.Comment: 13 pages, 5 figures,1 table. Accepted for publication by Research in
Astronomy and Astrophysic
Active inductor shunt peaking in high-speed VCSEL driver design
An all transistor active inductor shunt peaking structure has been used in a
prototype of 8-Gbps high-speed VCSEL driver which is designed for the optical
link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated
in a commercial 0.25-um Silicon-on-Sapphire (SoS) CMOS process for radiation
tolerant purpose. The all transistor active inductor shunt peaking is used to
overcome the bandwidth limitation from the CMOS process. The peaking structure
has the same peaking effect as the passive one, but takes a small area, does
not need linear resistors and can overcome the process variation by adjust the
peaking strength via an external control. The design has been tapped out, and
the prototype has been proofed by the preliminary electrical test results and
bit error ratio test results. The driver achieves 8-Gbps data rate as simulated
with the peaking. We present the all transistor active inductor shunt peaking
structure, simulation and test results in this paper.Comment: 4 pages, 6 figures and 1 table, Submitted to 'Chinese Physics C
Structural Behavior of Thin-Walled Concrete-Filled Steel Tube Used in Cable Tunnel: An Experimental and Numerical Investigation
One steel grid and five thin-walled concrete-filled steel tubes (CTST) used as the supports of tunnel were tested in site for investigating the mechanical behavior. The mechanical influences of thickness, node form, and concrete on CTST were gained and compared with the impacts on steel grid. It is indicated that high antideformation capacity of CTST improved the stability of surrounding rock in short time. The cementitious grouted sleeve connection exhibited superior flexibility when CTST was erected and built. Although the deformation of rock and soil in the tunnel was increasing, good compression resistance was observed by CTST with the new connection type. It was also seen that vault, tube foot, and connections were with larger absolute strain values. The finite element analysis (FEA) was carried out using ABAQUS program. The results were validated by comparison with experimental results. The FE model could be referred by similar projects
Radial Angular Momentum Transfer and Magnetic Barrier for Short-Type Gamma-Ray Burst Central Engine Activity
Soft extended emission (EE) following initial hard spikes up to 100 seconds
was observed with {\em Swift}/BAT for about half of short-type gamma-ray bursts
(SGRBs). This challenges the conversional central engine models of SGRBs, i.e.,
compact star merger models. In the framework of the black hole-neutron star
merger models, we study the roles of the radial angular momentum transfer in
the disk and the magnetic barrier around the black hole for the activity of
SGRB central engines. We show that the radial angular momentum transfer may
significantly prolong the lifetime of the accretion process and multiple
episodes may be switched by the magnetic barrier. Our numerical calculations
based on the models of the neutrino-dominated accretion flows suggest that the
disk mass is critical for producing the observed EE. In case of the mass being
, our model can reproduce the observed timescale and
luminosity of both the main and EE episodes in a reasonable parameter set. The
predicted luminosity of the EE component is lower than the observed EE with
about one order of magnitude and the timescale is shorter than 20 seconds if
the disk mass being . {\em Swift}/BAT-like instruments may
be not sensitive enough to detect the EE component in this case. We argue that
the EE component would be a probe for merger process and disk formation for
compact star mergers.Comment: 9 pages, 3 figures, accepted for publication in Ap
Graphene oxide nanoparticles for enhanced photothermal cancer cell therapy under the irradiation of a femtosecond laser beam
Nano-sized graphene and graphene oxide (GO) are promising for biomedical applications, such as drug delivery and photothermal therapy of cancer. It is observed in thiswork that the ultrafast reduction of GO nanoparticles (GONs)with a femtosecond laser beam creates extensive microbubbling. To understand the surface chemistry of GONs on the microbubble formation, the GONs were reduced to remove
most of the oxygen-containing groups to get reduced GONs
(rGONs). Microbubbling was not observed when the rGONs
were irradiated by the laser. The instant collapse of the
microbubbles may produce microcavitation effect that brings
about localized mechanical damage. To understand the
potential applications of this phenomenon, cancer cells
labeled with GONs or rGONs were irradiated with the laser.
Interestingly, the microbubbling effect greatly facilitated the
destruction of cancer cells. When microbubbles were produced,
the effective laser power was reduced to less than
half of what is needed when microbubbling is absent. This
finding will contribute to the safe application of femtosecond
laser in the medical area by taking advantage of the ultrafast
reduction of GONs. It may also find other important applications
that need highly localized microcavitation effects
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