351 research outputs found
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
Tracking Rates of Forest Disturbance and Associated Carbon Loss in Areas of Illegal Amber Mining in Ukraine Using Landsat Time Series
Mapping forest disturbance is crucial for many applications related to decision-making for sustainable forest management. This study identified the effect of illegal amber mining on forest change and accumulated carbon stock across a study area of 8125.5 ha in northern Ukraine. Our method relies on the Google Earth Engine (GEE) implementation of the Landsat-based Detection of Trends in Disturbance and Recovery (LandTrendr) temporal segmentation algorithm of Landsat time-series (LTS) to derive yearly maps of forest disturbance and recovery in areas affected by amber extraction operations. We used virtual reality (VR) 360 interactive panoramic images taken from the sites to attribute four levels of forest disturbance associated with the delta normalized burn ratio (dNBR) and then calculated the carbon loss. We revealed that illegal amber extraction in Ukraine has been occurring since the middle of the 1990s, yielding 3260 ha of total disturbed area up to 2019. This study indicated that the area of forest disturbance increased dramatically during 2013–2014, and illegal amber operations persist. As a result, regrowth processes were mapped on only 375 ha of total disturbed area. The results were integrated into the Forest Stewardship Council® (FSC®) quality management system in the region to categorize Forest Management Units (FMUs) conforming to different disturbance rates and taking actions related to their certification status. Moreover, carbon loss evaluation allows the responsible forest management systems to be streamlined and to endorse ecosystem service assessment
Fast barrier-free switching in synthetic antiferromagnets
We analytically solve the Landau-Lifshitz equations for the collective
magnetization dynamics in a synthetic antiferromagnet (SAF) nanoparticle and
uncover a regime of barrier-free switching under a short small-amplitude
magnetic field pulse applied perpendicular to the SAF plane. We give examples
of specific implementations for forming such low-power and ultra-fast switching
pulses. For fully optical, resonant, barrier-free SAF switching we estimate the
power per write operation to be pJ, 10-100 times smaller than for
conventional quasi-static rotation, which should be attractive for memory
applications.Comment: 12 pages, 4 figure
Topological photonics with scattering media
Scattering media, being ubiquitous in nature and critically important for
assessments (e.g., biological tissues), are often considered as nuisance in
optics. Here we show that it is not always the case and scattering media could
be essential in providing elements of topological photonics. We demonstrate
that topological darkness can be realised in the presence of scattering media
due to the transverse nature of electromagnetic waves and the hairy ball
theorem. We describe realizations of topological darkness in a scattering
medium comprising composite gold nanostructures produced by a low-cost
technique of laser structuring of thin metal films. Our results can be useful
for a variety of tasks, including topological nanophotonics, optical label-free
biosensing, and biomedical photonics
An alternative approach to the construction of Schur-Weyl transform
We propose an alternative approach for the construction of the unitary matrix
which performs generalized unitary rotations of the system consisting of
independent identical subsystems (for example spin system). This matrix, when
applied to the system, results in a change of degrees of freedom, uncovering
the information hidden in non-local degrees of freedom. This information can be
used, inter alia, to study the structure of entangled states, their
classification and may be useful for construction of quantum algorithms.Comment: 6 page
Electronic structure, optical and magnetic properties of CoFeGe Heusler alloy films
Optical properties of ferromagnetic half-metallic full-Heusler CoFeGe
alloy are investigated experimentally and theoretically. CoFeGe thin
films were obtained by DC magnetron sputtering and show the saturation
magnetization at =10 K of 5.6 /f.u., close to the value
predicted by the Slater-Pauling rule. First-principles calculations of the
electronic structure and the dielectric tensor are performed using the
full-potential linearized-augmented-plane-wave method in the generalized
gradient (GGA) and GGA+U approximations. The measured interband optical
conductivity spectrum for the alloy exhibits a strong absorption band in the 1
- 4 eV energy range with pronounced fine structure, which agrees well with the
calculated half-metallic spectrum of the system, suggesting a near perfect
spin-polarization in the material.Comment: 6 pages, 9 figure
Nanomechanical electro-optical modulator based on atomic heterostructures
Two-dimensional atomic heterostructures combined with metallic nanostructures allow one to realize strong light–matter interactions. Metallic nanostructures possess plasmonic resonances that can be modulated by graphene gating. In particular, spectrally narrow plasmon resonances potentially allow for very high graphene-enabled modulation depth. However, the modulation depths achieved with this approach have so far been low and the modulation wavelength range limited. Here we demonstrate a device in which a graphene/hexagonal boron nitride heterostructure is suspended over a gold nanostripe array. A gate voltage across these devices alters the location of the two-dimensional crystals, creating strong optical modulation of its reflection spectra at multiple wavelengths: in ultraviolet Fabry–Perot resonances, in visible and near-infrared diffraction-coupled plasmonic resonances and in the mid-infrared range of hexagonal boron nitride's upper Reststrahlen band. Devices can be extremely subwavelength in thickness and exhibit compact and truly broadband modulation of optical signals using heterostructures of two-dimensional materials
ПРОГРАМНИЙ КОМПЛЕКС ДЛЯ ОБРОБКИ СИНХРОННО ЗАРЕЄСТРОВАНИХ БІОСИГНАЛІВ У ПОЛІГРАФАХ
The work described a software package, which provides the compatible statistical processing simultaneously registered in the polygraph biosignals based on a model vector cyclical rhythm associated random processes.В работе описана разработка программного комплекса, который позволяет проводить совместную статистическую обработку синхронно зарегистрированных биосигналов в полиграфах на основе модели вектора циклических ритмично связанных случайных процессов.У роботі описано розробку програмного комплексу, який дає змогу проводити сумісну статистичну обробку синхронно зареєстрованих біосигналів в поліграфах на основі моделі вектора циклічних ритмічно пов'язаних випадкових процесів
Pro-russian propaganda recognition and analytics system based on text classification model and statistical data processing methods
In this paper a neural network model for classifying the political polarity of text has been developed, along with a database for training the neural network and an analytics system for pro-Russian propaganda. This allows to classify the political polarity of the message source based on its identifier, as well as to construct and display different networks that represent useful insights about popular Twitter hashtags or Telegram channels that related to Russo Ukrainian War. Also, a user interface has been developed that allows users to interact with the system. Developed system will help people with navigation through the information space and avoidance of pro-Russian propaganda
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