2,864 research outputs found
Optimization of Dimples in Microchannel Heat Sink with Impinging JetsâPart B: the Influences of Dimple Height and Arrangement
The combination of a microchannel heat sink with impinging jets and dimples (MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design
AT2019 avd: A tidal disruption event with a two-phase evolution
Tidal disruption events (TDEs) can uncover the quiescent super-massive black
holes (SMBHs) at the center of galaxies and also offer a promising method to
study them. After the disruption of a star by a SMBH, the highly elliptical
orbit of the debris stream will be gradually circularized due to the
self-crossing, and then the circularized debris will form an accretion disk.
The recent TDE candidate AT 2019avd has double peaks in its optical light
curve, and the X-ray emerges near the second peak. The durations of the peaks
are about 400 and 600 days, respectively, and the separation between them is ~
700 days. We fit and analyse its spectral energy distribution (SED) in
optical/UV, mid-infrared, and X-ray bands. We find that this source can be
interpreted as the circularization process in the first phase plus the delayed
accretion process in the second phase. Under this two-phase scenario, we use
the succession of self-crossing circularization model to fit the first peak,
and the delayed accretion model to fit the second peak. The fitting results are
consistent with the partial disruption of a 0.9 M_sun star by a 7 * 10^6 M_sun
SMBH with the penetration factor \beta ~ 0.6. Furthermore, we find the
large-amplitude (by factors up to ~ 5) X-ray variability in AT 2019avd can be
interpreted as the rigid-body precession of the misaligned disk due to the
Lense-Thirring effect of a spinning SMBH, with the disk precession period of 10
- 25 days.Comment: 14 pages, 11 figures, 4 tables, Submitted to Ap
The Power Spectra of Two Classes of Long-duration Gamma-ray Bursts
We have studied the averaged power density spectra (PDSs) of two classes of
long-duration gamma-ray bursts in the recent classification by Balastegui et
al.(2001) based on neural network analysis. Both PDSs follow a power law over a
wide frequency range with approximately the same slope, which indicates that a
process with a self-similar temporal property may underlie the emission
mechanisms of both. The two classes of bursts are divided into groups according
to their brightness and spectral hardness respectively and each group's PDS was
calculated; For both classes, the PDS is found to flatten both with increasing
burst brightness and with increasing hardness.Comment: 6 pages, 3 figures, a translated version from published in the Acta
Astronomica Sinica, to appear in the Chinese Astronomy & Astrophysics Vol.27,
Issue
Mechanisms Of Intrinsic Epileptogenesis In Human Gelastic Seizures With Hypothalamic Hamartoma
Human hypothalamic hamartoma (HH) is a rare developmental malformation often characterized by gelastic seizures, which are refractory to medical therapy. Ictal EEG recordings from the HH have demonstrated that the epileptic source of gelastic seizures lies within the HH lesion itself. Recent advances in surgical techniques targeting HH have led to dramatic improvements in seizure control, which further supports the hypothesis that gelastic seizures originate within the HH. However, the basic cellular and molecular mechanisms of epileptogenesis in this subcortical lesion are poorly understood. Since 2003, Barrow Neurological Institute has maintained a multidisciplinary clinical program to evaluate and treat patients with HH. This program has provided a unique opportunity to investigate the basic mechanisms of epileptogenesis using surgically resected HH tissue. The first report on the electrophysiological properties of HH neurons was published in 2005. Since then, ongoing research has provided additional insights into the mechanisms by which HH generate seizure activity. In this review, we summarize this progress and propose a cellular model that suggests that GABA-mediated excitation contributes to epileptogenesis in HH lesions
DNMT3a in the hippocampal CA1 is crucial in the acquisition of morphine selfâadministration in rats
Drugâreinforced excessive operant responding is one fundamental feature of long-lasting addictionâlike behaviors and relapse in animals. However, the transcriptional regulatory mechanisms responsible for the persistent drugâspecific (not natural rewards) operant behavior are not entirely clear. In this study, we demonstrate a key role for one of the de novo DNA methyltransferase, DNMT3a, in the acquisition of morphine selfâadministration (SA) in rats. The expression of DNMT3a in the hippocampal CA1 region but not in the nucleus accumbens shell was significantly upâregulated after 1â and 7âday morphine SA (0.3 mg/kg/infusion) but not after the yoked morphine injection. On the other hand, saccharin SA did not affect the expression of DNMT3a or DNMT3b. DNMT inhibitor 5âazaâ2âdeoxycytidine (5âaza) microinjected into the hippocampal CA1 significantly attenuated the acquisition of morphine SA. Knockdown of DNMT3a also impaired the ability to acquire the morphine SA. Overall, these findings suggest that DNMT3a in the hippocampus plays an important role in the acquisition of morphine SA and may be a valid target to prevent the development of morphine addiction.
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