Fast THz-TDS Reflection Imaging with ECOPS-Point-by-Point versus Line-by-Line Scanning.

We built a high-speed TDS setup with the use of electronically controlled optical sampling (ECOPS), which can measure up to 1600 terahertz pulses per second. The movement of the sample was provided by two fast-speed motorized linear stages constituting the gantry. We developed a flat-bar-based metal marker approach for the synchronization of continuous line-by-line scans. We carefully compared the performance of the terahertz reflection time-domain spectroscopy (TDS) scanner operating in a slow point-by-point and a one-hundred-times faster line-by-line imaging scheme. We analyzed images obtained for both schemes for a uniform metallic breadboard with holes, as well as a glass composite sample with defects. Although the measurement time was reduced by 100 times in terms of the line-by-line scheme, the overall performance in both schemes was almost identical in terms of the defects' sizes, shapes and locations. The results proved that the proposed ECOPS TDS system can provide uniform and extremely fast scanning without any deterioration in image quality.

Detection of Inflatable Boats and People in Thermal Infrared with Deep Learning Methods.

Smuggling of drugs and cigarettes in small inflatable boats across border rivers is a serious threat to the EU's financial interests. Early detection of such threats is challenging due to difficult and changing environmental conditions. This study reports on the automatic detection of small inflatable boats and people in a rough wild terrain in the infrared thermal domain. Three acquisition campaigns were carried out during spring, summer, and fall under various weather conditions. Three deep learning algorithms, namely, YOLOv2, YOLOv3, and Faster R-CNN working with six different feature extraction neural networks were trained and evaluated in terms of performance and processing time. The best performance was achieved with Faster R-CNN with ResNet101, however, processing requires a long time and a powerful graphics processing unit.

Benzyltrimethylammonium cadmium dicyanamide with polar order in multiple phases and prospects for linear and nonlinear optical temperature sensing.

Coordination polymers with multiple non-centrosymmetric phases have sparked substantial research efforts in the materials community. We report the synthesis and properties of a hitherto unknown cadmium dicyanamide coordination polymer comprising benzyltrimethylammonium cations (BeTriMe+). The room-temperature (RT) crystal structure of [BeTriMe][Cd(N(CN)2)3] (BeTriMeCd) is composed of Cd centers linked together by triple dca-bridges to form one-dimensional chains with BeTriMe+ cations located in void spaces between the chains. The structure is polar, the space group is Cmc21, and the spontaneous polarization in the c-direction is induced by an arrangement of BeTriMe+ dipoles. BeTriMeCd undergoes a second-order phase transition (PT) at T1 = 268 K to a monoclinic polar phase P21. Much more drastic structural changes occur at the first-order PT observed in DSC at T2 = 391 K. Raman data prove that the PT at T2 leads to extensive rearrangement of the Cd-dca coordination sphere and pronounced disorder of both dca and BeTriMe+. On cooling, the HT polymorph transforms at T3 = 266 K to another phase of unknown symmetry. Temperature-resolved second harmonic generation (TR-SHG) studies at 800 nm confirm the structural non-centrosymmetry of all the phases detected. Optical studies indicate that BeTriMeCd exhibits at low temperatures an intense emission under 266 nm excitation. Strong temperature dependence of both one-photon excited luminescence and SHG response allowed for the demonstration of two disparate modes of optical thermometry for a single material. One is the classic ratiometric luminescence thermometry employing linear excitation in the ultraviolet region while the other is single-band SHG thermometry, a thus far unprecedented subtype of nonlinear optical thermometry. Thus, BeTriMeCd is a rare example of a dicyanamide framework exhibiting polar order, SHG activity, photoluminescence properties and linear and nonlinear optical temperature sensing capability.

Characterization of prospective explosive materials using terahertz time-domain spectroscopy.

We investigated six prospective explosive materials in the terahertz range using time-domain spectroscopy. A family of energetic azotetrazolate salts and two caged nitramines were studied. A number of distinct spectral features were observed in the 0.8-3.2 THz frequency range. In transmission configuration in ambient temperature, we determined the absorption coefficient and the refractive index of the materials, which were compressed as pellets. Because the visibility of some absorption peaks was not clear, additionally we performed characterization of these materials in a temperature range from -175°C to 0°C, which resulted in highlighting peaks with low amplitude. Because the considered explosives are insensitive to compression, we also measured them using an attenuated total reflection (ATR) technique, in which sample preparation is easier than with pressed pellets. The absorption peaks measured by ATR agree well with those determined in transmission. This suggests that ATR also can be used for identification of these classes of materials.

3D printed diffractive terahertz lenses.

A 3D printer was used to realize custom-made diffractive THz lenses. After testing several materials, phase binary lenses with periodic and aperiodic radial profiles were designed and constructed in polyamide material to work at 0.625 THz. The nonconventional focusing properties of such lenses were assessed by computing and measuring their axial point spread function (PSF). Our results demonstrate that inexpensive 3D printed THz diffractive lenses can be reliably used in focusing and imaging THz systems. Diffractive THz lenses with unprecedented features, such as extended depth of focus or bifocalization, have been demonstrated.

TRPM7 channels in hippocampal neurons detect levels of extracellular divalent cations.

Exposure to low Ca(2+) and/or Mg(2+) is tolerated by cardiac myocytes, astrocytes, and neurons, but restoration to normal divalent cation levels paradoxically causes Ca(2+) overload and cell death. This phenomenon has been called the "Ca(2+) paradox" of ischemia-reperfusion. The mechanism by which a decrease in extracellular Ca(2+) and Mg(2+) is "detected" and triggers subsequent cell death is unknown. Transient periods of brain ischemia are characterized by substantial decreases in extracellular Ca(2+) and Mg(2+) that mimic the initial condition of the Ca(2+) paradox. In CA1 hippocampal neurons, lowering extracellular divalents stimulates a nonselective cation current. We show that this current resembles TRPM7 currents in several ways. Both (i) respond to transient decreases in extracellular divalents with inward currents and cell excitation, (ii) demonstrate outward rectification that depends on the presence of extracellular divalents, (iii) are inhibited by physiological concentrations of intracellular Mg(2+), (iv) are enhanced by intracellular phosphatidylinositol 4,5-bisphosphate (PIP(2)), and (v) can be inhibited by Galphaq-linked G protein-coupled receptors linked to phospholipase C beta1-induced hydrolysis of PIP(2). Furthermore, suppression of TRPM7 expression in hippocampal neurons strongly depressed the inward currents evoked by lowering extracellular divalents. Finally, we show that activation of TRPM7 channels by lowering divalents significantly contributes to cell death. Together, the results demonstrate that TRPM7 contributes to the mechanism by which hippocampal neurons "detect" reductions in extracellular divalents and provide a means by which TRPM7 contributes to neuronal death during transient brain ischemia.

Insulin increases the potency of glycine at ionotropic glycine receptors.

The mechanisms by which insulin modulates neuronal plasticity and pain processes remain poorly understood. Here we report that insulin rapidly increases the function of glycine receptors in murine spinal neurons and recombinant human glycine receptors expressed in human embryonic kidney cells. Whole-cell patch-clamp recordings showed that insulin reversibly enhanced current evoked by exogenous glycine and increased the amplitude of spontaneous glycinergic miniature inhibitory postsynaptic currents recorded in cultured spinal neurons. Insulin (1 microM) also shifted the glycine concentration-response plot to the left and reduced the glycine EC(50) value from 52 to 31 microM. Currents evoked by a submaximal concentration of glycine were increased to approximately 140% of control. The glycine receptor alpha subunit was sufficient for the enhancement by insulin because currents from recombinant homomeric alpha(1) receptors and heteromeric alpha(1)beta receptors were both increased. Insulin acted at the insulin receptor via pathways dependent on tyrosine kinase and phosphatidylinositol 3 kinase because the insulin effect was eliminated by the insulin receptor antagonist, hydroxy-2-naphthalenylmethylphosphonic acid trisacetoxymethyl ester, the tyrosine kinase inhibitor lavendustin A, and the phosphatidylinositol 3 kinase antagonist wortmannin. Together, these results show that insulin has a novel regulatory action on the potency of glycine for ionotropic glycine receptors.