2,276 research outputs found
Modification of a polyamide reverse osmosis membrane by heat treatment for enhanced fouling resistance
The use of heat treatment to improve solute rejection and fouling resistance of a polyamide reverse osmosis (RO) membrane was investigated in this study. Heat treatment was carried out by immersing the membrane samples in Milli-Q water at 70 degrees celcius for a specific duration. Heat treatment reduced the pure water permeability from 4.1 to 2.8 L/m2 bar but improved conductivity rejection from 95.5 to 97.0 percent. As a result, a correlation was observed between changes in the two parameters. Marginal changes in the membrane surface characteristics were observed as a result of heat treatment. Heat treatment significantly improved the fouling resistance property of the RO membrane. When the secondary effluent was filtrated at an elevated permeated flux, the virgin RO membrane exhibited 30 percent flux decline while the heat-treated membrane showed only 12 percent flux decline. This is possibly because heat treatment resulted in a denser cross-linked active skin layer, thus reducing the blockage caused by small organic foulants
Critical enhancement of thermopower in a chemically tuned polar semimetal MoTe
Ferroelectrics with spontaneous electric polarization play an essential role
in today's device engineering, such as capacitors and memories. Their physical
properties are further enriched by suppressing the long-range polar order, as
is exemplified by quantum paraelectrics with giant piezoelectric and dielectric
responses at low temperatures. Likewise in metals, a polar lattice distortion
has been theoretically predicted to give rise to various unusual physical
properties. So far, however, a "ferroelectric"-like transition in metals has
seldom been controlled and hence its possible impacts on transport phenomena
remain unexplored. Here we report the discovery of anomalous enhancement of
thermopower near the critical region between the polar and nonpolar metallic
phases in 1T'-MoNbTe with a chemically tunable polar
transition. It is unveiled from the first-principles calculations and
magnetotransport measurements that charge transport with strongly
energy-dependent scattering rate critically evolves towards the boundary to the
nonpolar phase, resulting in large cryogenic thermopower. Such a significant
influence of the structural instability on transport phenomena might arise from
the fluctuating or heterogeneous polar metallic states, which would pave a
novel route to improving thermoelectric efficiency.Comment: 26 pages, 4 figure
Magnetic and orbital order in overdoped bilayer manganites
The magnetic and orbital orders for the bilayer manganites in the doping
region have been investigated from a model that incorporates the
two orbitals at each Mn site, the inter-orbital Coulomb interaction and
lattice distortions. The usual double exchange operates via the orbitals.
It is shown that such a model reproduces much of the phase diagram recently
obtained for the bilayer systems in this range of doping. The C-type phase with
() spin order seen by Ling et al. appears as a natural consequence
of the layered geometry and is stabilised by the static distortions of the
system. The orbital order is shown to drive the magnetic order while the
anisotropic hopping across the orbitals, layered nature of the underlying
structure and associated static distortions largely determine the orbital
arrangements.Comment: 8 pages, 5 figure
Extracranial-intracranial bypass in atherosclerotic cerebrovascular disease: Report of a single centre experience
Despite the failure of the international extracranial-intracranial (EC-IC) bypass study in showing the benefit of bypass procedure for prevention of stroke recurrence, it has been regarded to be beneficial in a subgroup of well-selected patients with haemodynamic impairment. This report includes the EC-IC bypass experience of a single centre over a period of 14 years. All consecutive 72 patients with atherosclerotic occlusive cerebrovascular lesions associated with haemodynamic compromise treated by EC-IC bypass surgery were retrospectively reviewed. Pre-operatively, 61% of patients presented with minor stroke and the remaining 39% with recurrent transient ischemic attacks (TIAs) despite maximal medical therapy. Angiography revealed a unilateral internal carotid artery (ICA) stenosis/occlusion in 79%, bilateral ICA stenosis/occlusion in 15%, MCA stenosis/occlusion in 3% and other multiple vessel stenosis/occlusion in 3% of the cases. H(2)(15)O positron emission tomography (PET) or 99mTc-HMPAO SPECT with acetazolamide challenge was performed for haemodynamic evaluation of the cerebral blood flow (CBF). All the patients had impaired haemodynamics pre-operatively in terms of reduced regional cerebrovascular reserve capacity and rCBF. Standard STA-MCA bypass procedure was performed in all patients. A total of 68 patients with 82 bypasses were reviewed with a mean follow-up period of 34 months. Stroke recurrence took place in 10 patients (15%) resulting in an annual stroke risk of 5%. Improved cerebral haemodynamics was documented in 81% of revascularised hemispheres. Patients with unchanged or worse haemodynamic parameters had significantly more post-operative TIAs or strokes when compared to those with improved perfusion reserves (30% vs.5% of patients, p<0.05). In conclusion, EC-IC bypass procedure in selected patients with occlusive cerebrovascular lesions associated with haemodynamic impairment has revealed to be effective for prevention of further cerebral ischemia, when compared with a stroke risk rate of 15% reported to date in patients only under antiplatelet agents or anticoagulant therapy
Information Security as Strategic (In)effectivity
Security of information flow is commonly understood as preventing any
information leakage, regardless of how grave or harmless consequences the
leakage can have. In this work, we suggest that information security is not a
goal in itself, but rather a means of preventing potential attackers from
compromising the correct behavior of the system. To formalize this, we first
show how two information flows can be compared by looking at the adversary's
ability to harm the system. Then, we propose that the information flow in a
system is effectively information-secure if it does not allow for more harm
than its idealized variant based on the classical notion of noninterference
Angular Momentum of Fission Products in 232Th+p System (II)
開始ページ、終了ページ: 冊子体のページ付
25 kHz narrow spectral bandwidth of a wavelength tunable diode laser with a short waveguide-based external cavity
We report on the spectral properties of a diode laser with a tunable external
cavity in integrated optics. Even though the external cavity is short compared
to other small-bandwidth external cavity lasers, the spectral bandwidth of this
tunable laser is as small as 25 kHz (FWHM), at a side-mode suppression ratio
(SMSR) of 50 dB. Our laser is also able to access preset wavelengths in as
little as 200 us and able to tune over the full telecom C-band (1530 nm - 1565
nm).Comment: 8 pages, 7 figure
Timing of Pleistocene glaciations in the High Atlas, Morocco: new 10Be and 36Cl exposure ages
This paper presents data from 42 new samples yielding Late Pleistocene cosmogenic 10Be and 36Cl exposure ages of moraine boulders across a series of glaciated valleys in the Toubkal Massif (4167 m a.s.l.), High Atlas, Morocco. This represents the first comprehensive Pleistocene glacial chronology in North Africa and one of the largest datasets from the Mediterranean region. The timing of these glacier advances has major implications for understanding the influence of Atlantic depressions on moisture supply to North Africa and the Mediterranean basin during the Pleistocene. The oldest and lowest moraines which span elevations from ∼1900 to 2400 m a.s.l. indicate that the maximum glacier advance occurred from MIS 5 to 3 with a combined mean 10Be and 36Cl age of 50.2 ± 19.5 ka (1 SD; n = 12, 7 outliers). The next moraine units up-valley at higher elevations (∼2200–2600 m a.s.l.) yielded exposure ages close to the global Last Glacial Maximum (LGM) with a combined mean 10Be and 36Cl age of 22.0 ± 4.9 ka (1 SD; n = 9, 7 outliers). The youngest exposure ages are from moraines that were emplaced during the Younger Dryas with a combined mean 10Be and 36Cl age of 12.3 ± 0.9 ka (1 SD; n = 7, no outliers) and are found in cirques at the highest elevations ranging from ∼2900 to 3300 m a.s.l. From moraines predating the Younger Dryas, a large number of young outliers are spread evenly between 6 and 13 ka suggesting a continuing process of exhumation or repositioning of boulders during the early to mid-Holocene. This attests to active seismic processes and possibly intense erosion during this period
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