The development of a novel polybutylene terephthalate (PBT) feedstock material for powder bed fusion of polymers with laser beam (PBF-LB/P) by means of liquid-liquid phase separation (LLPS) and ...precipitation is outlined. Appropriate solvents for precipitation have been identified by a screening approach based on solubility parameters. Feasible system compositions and solution and cloud point temperatures were determined. For the most promising solvent, cyclopentanone, a parameter study on the influence of stirring conditions during precipitation was performed. The obtained products were characterized with respect to their particle size distribution, particle shape, phase morphology, thermal properties and melt viscosity. Under optimized process conditions, PBT particles of high degree of crystallinity with narrow size distribution and a mean diameter of 36 μm were obtained; flowability was improved by dry coating. The initial PBF-LB/P processability was assessed by building single layers in a parameter study using a Formiga P110 machine. Dense single layers were obtained at laser power PL = 11.5 W, scanning speed vS = 4000 mm/s, hatch distance hS = 0.24 mm and layer thickness dS = 0.1 mm. Best to the authors' knowledge, this is the first study in the open literature reporting on a PBT feedstock material obtained by liquid-liquid phase separation and crystallization.
Display omitted
•Development of PBT PBF feedstock with narrow size distribution, high roundness and circularity produced via precipitation.•PBT feedstock material of good flowability, high degree of crystallinity and broad PBF processing window.•Solubility parameter screening and cloud point measurement for polymer-solvent system and process condition identification.•Thorough characterization of developed PBT feedstock powder with respect to thermal, rheological and bulk solid properties.•Derivation of PBF process parameters for the precipitated PBF feedstock via parameter study on a commercial PBF machine.
Plasmonic gallium (Ga) nanoparticles (NPs) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to ...reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narrowing the NP size distribution among other factors. With this purpose, our last work demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region. The quantitative analysis of the optical properties by spectroscopic ellipsometry confirmed an outstanding improvement of the LSPR intensity and full width at half maximum (FWHM) due to the imposed ordering. Here, by engineering the template dimensions, and therefore by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions. More interestingly, the factors that cause this optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. The results allow us to conclude that the plasmonic coupling between NPs originated in the ordered systems is the main cause for the optimized optical response.
Microbial biofilms frequently cause the esthetic and biological deterioration of stone monuments. Chichén Itzá, designated as a UNESCO World Heritage Site and as one of the seven new wonders of the ...world, is one Maya archeological site affected by biofilms. In the present study, we analyzed the biofilms at three different building complexes of Chichén Itzá: the Lower Temple of the Jaguars, the Temple of the Warriors, and Tzompantli. Samples of biofilms and detached rocks were taken from walls with abundant white-, green-, black-, and orange-colored biofilms. The morphology of rock fragments and dust was analyzed by electron and optical microscopy and was structurally characterized by X-ray diffraction. An HCl treatment (5% v/v) was subsequently applied to eliminate carbonates. The morphological analysis evidenced the presence of cyanobacteria, algae, and lichens. Some algae formed small nodules on orange- or black-colored rocks. Lichens were associated with a distinct mineral content on the inner surface of rocks versus on the outer surface. The presence of calcium oxalates such as weddellite (C
2
CaO
4
·2H
2
O) and whewellite (C
2
CaO
4
·H
2
O) and other minerals, including quartz and feldspars, was confirmed by X-ray diffraction. The lichens collected from the Lower Temple of the Jaguars and Tzompantli were therefore confirmed to disintegrate rock surfaces through biomineralization and the formation of oxalate crystals. At sites with greater solar radiation, a higher quantity of weddellite and a lower quantity of whewellite were observed. In conclusion, the establishment of microorganisms on the stone surfaces of Chichén Itzá causes esthetic damage and also leads to the biomineralization of these rock surfaces.
Abstract
The specific loss power (SLP) is a figure of merit in nanomagnetism, which allows to classify systems of magnetic nanoparticles (MNPs) according to their capability to dissipate heating ...power in response to the energy absorbed from an alternating magnetic field (AMF) at radiofrequencies. SLP magnitude is relevant in biological applications of MNPs, such as nanomedicine, where the thermal energy released by these nanostructures can be used to produce apoptosis in cancer cells, becoming a promising alternative for the treatment of malignant tumors. In this work we present details of the design and construction of a lab-made electromagnetic system to perform SLP measurements in systems of MNPs. The system is composed by an actuation stage, which generates the AMF to excite the sample, a thermal insulation stage between the sample and its surroundings, and two sensing stages: the first one for measuring the magnetic field applied to the sample and the second one for measuring the changes of temperature of the sample. The system developed allows to reach AMFs around 7.7 kA m
−1
in the center of the actuation coil, operating at 260 kHz and with a power consumption less than 150 W. The architecture of the system allows the automatization and control of SLP measurements from remote places through the IEEE 488 bus available in the power source and a graphic interface developed in LabVIEW software, which allows to visualize temperature versus time measurements, control the magnetic field amplitude and store the data in a public folder available in the cloud. Some results are presented, where the system is employed to measure the SLP of a colloidal suspension of MNPs of maghemite (
γ
-Fe
2
O
3
) stabilized with sodium polyacrylate. The results obtained show a satisfactory performance of the device to measure the SLP of samples of MNPs for different purposes.
Summary
UV‐B radiation inhibits plant growth, and this inhibition is, to a certain extent, regulated by miR396‐mediated repression of Growth Regulating Transcription factors (GRFs). Moreover, E2Fe ...transcription factor also modulates Arabidopsis leaf growth. Here, we provide evidence that, at UV‐B intensities that induce DNA damage, E2Fc participates in the inhibition of cell proliferation. We demonstrate that E2Fc‐deficient plants show a lower inhibition of leaf size under UV‐B conditions that damage DNA, decreased cell death after exposure and altered SOG1 and ATR expression. Interestingly, the previously reported participation of E2Fe in UV‐B responses, which is a transcriptional target of E2Fc, is independent and different from that described for E2Fc. Conversely, we here demonstrate that E2Fc has an epistatic role over the miR396 pathway under UV‐B conditions. Finally, we show that inhibition of cell proliferation by UV‐B is independent of the regulation of class II TCP transcription factors. Together, our results demonstrate that E2Fc is required for miR396 activity on cell proliferation under UV‐B, and that its role is independent of E2Fe, probably modulating DNA damage responses through the regulation of SOG1 and ATR transcript levels.
Significance Statement
At intensities that can induce DNA damage in Arabidopsis plants, E2Fc‐deficient plants show a lower inhibition of leaf size and an altered DNA damage response. The inhibition of plant growth by UV‐B mediated by E2Fc occurs epistatically over the microRNA396 and independently of E2Fe.
This work presents a detailed analysis of the performance of X‐ray magnetic circular dichroism photoemission electron microscopy (XMCD‐PEEM) as a tool for vector reconstruction of magnetization. For ...this, 360° domain wall ring structures which form in a synthetic antiferromagnet are chosen as the model to conduct the quantitative analysis. An assessment is made of how the quality of the results is affected depending on the number of projections that are involved in the reconstruction process, as well as their angular distribution. For this a self‐consistent error metric is developed which allows an estimation of the optimum azimuthal rotation angular range and number of projections. This work thus proposes XMCD‐PEEM as a powerful tool for vector imaging of complex 3D magnetic structures.
The performance of X‐ray magnetic circular dichroism photoemission electron microscopy for vector imaging of complex three‐dimensional magnetic textures is investigated.
The present paper describes the use of a microfluidic system to synthesize carbon dots (Cdots) and their use as optical pH sensors. The synthesis is based on the thermal decomposition of ascorbic ...acid in dimethyl sulfoxide. The proposed microsystem is composed of a fluidic and a thermal platform, which enable proper control of synthesis variables. Uniform and monodispersed 3.3 nm-sized Cdots have been synthesized, the optical characterization of which showed their down/upconversion luminescence and colorimetric properties. The obtained Cdots have been used for pH detection with down and upconverison fluorescent properties as excitation sources. The naked eye or a photographic digital camera has also been implemented as detection systems with the hue parameter showing a linear pH range from 3.5 to 10.2. On the other hand, experiments on the cytotoxicity and permeability of the Cdots on human embryonic kidney cells revealed their adsorption on cells without causing any impact on the cellular morphology.
The paper describes the use of a microfluidic system to synthesize carbon dots and their use as optical pH sensors.
•We achieve control of the dynamics of a spin chain at times near the QSL with one or two actuators.•The control schemes are robust against static disorder achieving near perfect state ...transfer.•Optimal Control Theory provides simple, reliable and efficient pulses to control excitations transfer in spin chains.
The Quantum Speed Limit (QSL) can be found in many different situations, in particular in the propagation of information through quantum spin chains. In homogeneous chains it implies that taking information from one extreme of the chain to the other will take a time O(N/2), where N is the chain length. Using Optimal Control Theory we design control pulses that achieve near perfect population transfer between the extremes of the chain at times on the order of N/2. Our results show that the control pulses that govern the dynamical behavior of chains with different lengths are closely related. The pulses were constructed for control schemes involving one or two actuators in chains with exchange couplings without static disorder. Our results also show that the two actuator scheme is considerably more robust against the presence of static disorder than the scheme that uses just a single one.
Based on colony spreading, chitosan from shrimp waste in agar media inhibited the growth of
Aspergillus niger by 47.26%; there were not differences (
P
>
0.05) with respect to commercial chitosan ...(Fluka, BioChemika) (56.16%). All chitosan films showed similar glass transition temperatures (
P
>
0.05) with respect to cellophane control; however, chemically, all chitosan films showed an increase in the
T
g values that could be related with the decrease (
P
≤
0.05) in elongation percentage with respect to the control film. According to FT-IR spectroscopic analysis of chitosan films, the fungistatic activity can be related to the hydrogen bonds’ formation between the amino groups of chitosan with the hydroxyl groups from polymer or sorbitol. The plasticizer addition increased (
P
≤
0.05) the elongation of chitosan films. The Young's module,
E, was lower (
P
≤
0.05) for all chitosan films comparing with cellophane. When incorporated into the composite films elaborated by casting, chitosan retained its fungistatic activity. Even though the activity against fungi growth was lower (15.66% for non-plasticized silage chitosan films, pC
S), a reduction (
P
≤
0.05) in the hyphae diameter of
A. niger was observed. Results suggest that it is feasible to elaborate antifungal chitosan films, with good thermal stability and acceptable mechanical properties for food packaging.
PDF
