Intensity-tunable terahertz bandpass filters based on liquid crystal integrated metamaterials.

In this paper, we demonstrate an intensity-tunable THz bandpass filter by introducing liquid crystal (LC) integrated with asymmetric frequency selective surface (FSS) and subwavelength metal gratings. Here, the tunable THz filter is derived from the inner polarization state conversion in composited devices, and the incident linear polarization can be converted into 90° orthogonal components. By controlling the LC orientation under the applied electric field with the metamaterial electrodes, the polarization conversion process can be actively modulated; thus, the polarization-dependent and tunable THz bandpass filter is achieved. Based on the multilayer design and the inner Fabry-Perot-like resonance mechanism, the LC-integrated metamaterials filter presents better filtering performance than the single FSS filter, and the Q-value is improved from 7.7 to 13.8 at the working frequency. Our simulated work paves the way for the design of new and efficient THz filters.

Multi-band terahertz linear polarization converter based on carbon nanotube integrated metamaterial.

Herein, we fabricated and investigated the carbon nanotube (CNT) integrated metamaterial for orthogonal polarization control in the THz regime, which is composed of a sandwiched CNT layer with the adjacent metal gratings in the sub-wavelength integration. Under the mechanism of multilayer polarization selection and multiple reflections in CNT constructed micro-cavity, the perfect orthogonal polarization conversion is achieved and the transmittance spectrum presents multi-band peaks and valleys, which coincide with the theoretical Fabry-Perot resonance. Besides, by controlling the layer number and orientations of the middle CNT, the active modulation of the amplitude and phase in compound metamaterials are realized. Based on the simulation of CNT in the grating model, it obtains a good agreement with the experimental results, and the simulated electric field distribution also confirmed the inner polarization conversion mechanism. This work combines nanomaterials with optical microstructures and successfully applies them to the THz polarization control, which will bring new ideas for design novel THz devices.

Terahertz resonance switch induced by the polarization conversion of liquid crystal in compound metasurface.

We experimentally demonstrate an active terahertz (THz) resonance switch induced by the polarization conversion in a compound metasurface, which is a LC layer sandwiched by a metallic wire grating and resonance metamaterial (LCGM). Here, the liquid crystal (LC) plays the role of polarization conversion, which can induce the TE resonance. Moreover, there exists a localized resonance between metallic grating and metamaterial layers, and then the excited resonance will be greatly enhanced. The results show that the high extinction ratio of the resonance switch exceeds 30 dB at 0.82 THz. This work will bring new ideas for the research in developing THz phase, polarization, and switch devices with LC and metasurface.

Wideband sub-THz half-wave plate using 3D-printed low-index metagratings with superwavelength lattice.

High-index dielectric metasurfaces are rarely reported around 0.1-0.3 THz, as an extremely large etching depth is needed according to the millimeter-scale wavelength. In this work, we propose an easy solution to sub-THz wideband polarization control by utilizing 3D-printed low-index (n~1.5) metagratings. The metagrating with subwavelength lattice is shown as a very efficient half-wave plate (net polarization conversion of 87%) at 0.14 THz but showing noisy spectrum. The design with superwavelength lattice offers a smooth and wide bandwidth for linear polarization rotation. Study of the mechanism shows that the lattice size slightly above wavelength is a better choice for the low-index metadevice as it maintains high efficiency in the zero diffraction order and wide bandwidth due to the small mode dispersion. Such designs offer a feasible solution especially suitable for sub-THz polarization and phase control, complementary to the existing high-index dielectric and metallic metasurfaces.

Mechanical modulation of terahertz wave via buckled carbon nanotube sheets.

Manipulation of terahertz (THz) wave plays an important role in THz imaging, communication, and detection. The difficulty in manipulating the THz wave includes single function, untunable, and inconvenient integration. Here, we present a mechanically tunable THz polarizer by using stretchable buckled carbon nanotube sheets on natural rubber substrate (BCNTS/rubber). The transmittance and degree of polarization of THz wave can be modulated by stretching the BCNTS/rubber. The experiments showed that the degree of polarization increased from 17% to 97%, and the modulation depth reached 365% in the range of 0.2-1.2 THz, as the BCNTS/rubber was stretched from 0% to 150% strain. These changes can be also used for high strain sensing up to 150% strain, with a maximum sensitivity of 2.5 M/S. A spatial modulation of THz imaging was also realized by stretching and rotating BCNTS/rubber. The theoretical analysis and numerical modeling further confirm the BCNTS/rubber changes from weak anisotropic to highly anisotropic structure, which play key roles in THz wave modulation. This approach for active THz wave manipulation can be widely used in polarization imaging, wearable material for security, and highly sensitive strain sensing.

Tunable terahertz wave-plate based on dual-frequency liquid crystal controlled by alternating electric field.

In this work, the optically anisotropic property of dual-frequency liquid crystals (DFLC) in terahertz (THz) regime has been experimentally investigated, which indicates that the refractive index and birefringence of DFLC can be continuously modulated by both the alternating frequency and intensity of the alternating electric field. This tunability originates from the rotation of DFLC molecules induced by alternating electric fields. The results show that by modulating the alternating frequency from 1 kHz to 100 kHz under 30 kV/m electric field, the 600 µm thickness DFLC cell can play as a tunable quarter-wave plate above 0.68 THz, or a half-wave plate above 1.33 THz. Besides, it can be viewed as a tunable THz phase shifter from 0 to π. Therefore, due to its novel tuning mechanism, DFLC will be of great significance in dynamic manipulating on THz phase and polarization.

Artificial high birefringence in all-dielectric gradient grating for broadband terahertz waves.

Subwavelength dielectric gratings are widely applied in the phase and polarization manipulation of light. However, the dispersion of the normal dielectric gratings is not flat while their birefringences are not enough in the THz regime. In this paper, we have fabricated two all-dielectric gratings with gradient grids in the THz regime, of which artificial birefringence is much larger than that of the equal-grid dielectric grating demonstrated by both experiments and simulations. The transmission and dispersion characteristics are also improved since the gradient grids break the periodicity of grating lattices as a chirp feature. From 0.6-1.4 THz, a broadband birefringence reaches 0.35 with a low dispersion and good linearity of phase shift, and the maximum phase shift is 1.4π. Furthermore, these gradient gratings are applied as half-wave plates and realize a linear polarization conversion with a conversion rate over 99%, also much higher than the equal-grid gratings. These gradient gratings show great advantages compared to the periodic gratings and provide a new way in the designing of artificial birefringence material.

Terahertz polarization converter and one-way transmission based on double-layer magneto-plasmonics of magnetized InSb.

In this work, we investigate the nonreciprocal circular dichroism for terahertz (THz) waves in magnetized InSb by the theoretical calculation and numerical simulation, which indicates that longitudinally magnetized InSb can be applied to the circular polarizer and nonreciprocal one-way transmission for the circular polarization THz waves. Furthermore, we propose a double-layer magnetoplasmonics based on the longitudinally magnetized InSb, and find two MO enhancement mechanisms in this device: the magneto surface plasmon resonance on the InSb-metal surface and Fabry-Pérot resonances between two orthogonal metallic gratings. These two resonance mechanisms enlarge the MO polarization rotation and greatly reduce the external magnetic field below 0.1T. The one-way transmission and perfect linear polarization conversion can be realized over 70dB, of which the transmittance can be modulated from 0 to 80% when the weak magnetic field changes from 0 to 0.1T under the low temperature around 200K. This magnetoplasmonic device has broad potential as a THz isolator, modulator, polarization convertor, and filter in the THz application systems.

Effects of intrahippocampal GABAB receptor antagonist treatment on the behavioral long-term potentiation and Y-maze learning performance.

GABAB receptor is present at pre- and post-synaptic sites and participates in many brain functions including cognition, reward and anxiety. Although a lot of research has shown that activation or blockade of GABAB receptor may produce different even opposing effects on long-term potentiation (LTP) and cognitive function, there is little information available concerning the effect of GABAB receptor on behavioral LTP, a learning-induced LTP model. Herein, we firstly examined the effects of 2-OH saclofen, a GABAB receptor antagonist, on the induction of behavioral LTP and Y-maze learning performance. In addition, GABAB receptor has been reported to be present on cholinergic terminals and to regulate the ACh release. Therefore, we also investigated the effect of 2-OH saclofen on the impairments in behavioral LTP and cognitive function induced by scopolamine, an acetylcholine receptor antagonist. We found that intrahippocampal application of 2-OH saclofen could significantly enhance the population spike (PS) amplitude with a dose-response relationship, and 20 µM 2-OH saclofen evidently facilitated the formation of behavioral LTP in the perforant pathway to the dentate gyrus (PP-DG) and led to an obvious improvement in maze learning performance. Furthermore, intrahippocampal 20 µM 2-OH saclofen administration could markedly reverse the scopolamine-induced impairments in behavioral LTP and maze performance. Our data demonstrate that blockade of GABAB receptor displays a facilitatory role in the induction of behavioral LTP and maze learning task, and the antagonist of GABAB receptor seems to exert the potentially therapeutic value in the cognitive defect induced by cholinergic dysfunction.

Effects of intrahippocampal L-NAME treatment on the behavioral long-term potentiation in dentate gyrus.

Using a combination of electrophysiological recordings, behavioral tests and local pharmacological administration in hippocampus, we investigated in the present study the effects of nitric oxide (NO) synthase inhibitor N-nitro-l-arginine methyl ester (l-NAME) on the behavioral long-term potentiation (LTP) and maze learning performance in freely moving rats. The results showed as follows: (1) intrahippocampal l-NAME administration led to a defect in maze learning performance of the animals; (2) l-NAME treatment also substantially impaired the induction of the behavioral LTP in perforant pathway to dentate gyrus (PP-DG) pathway induced by maze learning task, while it had no significant effects on basic synaptic transmission in PP-DG pathway; Collectively, these results indicate that NO synthesis may be critical for the behavioral LTP in PP-DG pathway and maze learning performance.

[Short-term outcome of the acellular dermal matrix in dental implant surgical sites].

OBJECTIVE: To evaluate the clinical short-term results of the acellular dermal matrix for guided bone regeneration. METHODS: Sixty-four patients with bone defect in anterior maxillary area (average bone width: 3 mm) were included. Ridge-splitting technique with simultaneous placement of implants and artificial bone material implantation was performed in 21 patients (non-membrane group). Forty-three patients received the same procedure but with acellular dermal matrix covering the surgical sites (membrane group). The patients were followed up for three months and the new bone formation was checked in clinic and by X-ray. RESULTS: Three months after operation, the membrane group showed good osseointegration and high bone density over the implant cover screws. In the second operation, the membranes became thinner and the new bone fully covered the implant in the membrane group. The labial bone exhibited slight absorption and labial surface of 7 implants in 7 patients was exposed in non-membrane group. The width and the height of the ridge in the second operation were greater in membrane group than in non-membrane group (P < 0.05). CONCLUSIONS: The acellular dermal matrix can effectively resist the growth of soft tissue to allow bone regeneration around the implant.

[Clinical application of maxillary sinus lift with Summers osteotome].

OBJECTIVE: To introduce and evaluate the procedure and the effect of maxillary sinus lift with closed technique by Summers osteotome, bone grafting and simultaneous implant placement. METHODS: 66 cases with severely resorbed alveolar bone in maxillary posterior region received sinus lift with Summers osteotome, simultaneously bone grafting and implants placement. The final restoration was finished at 6 months postoperatively. RESULTS: The operation procedure were eventless in the 66 cases, the sinus floor were elevated by 2-5 mm, three-dimensional reconstruction of the CT scan pictures showed the smooth dome profile of the lifting sites and no signs of laceration on the membrane, and there were no maxillary antritis after operation. After 6 months, no significantly bone graft resorption and good osseointegration were noticed in X-ray imaging. The final restoration was finished at this time. 12-24 months after the restoration, all implants inserted were remain, the hard and soft tissue were healthy, prosthesis were stable and functioned. X-ray showed good osseointegration in the lifting sites, the vertical resorption around the implants were less than 1 mm. CONCLUSION: With properly use of Summers osteotome, scraps of the bone in the implant sockets can be pushed into the sinus, these autogenous bone scraps were in favor of the osseogenesis and the sinus floor can be easily elevated by the method with very infrequent complications. It enlarged indication of dental implants and avoided operation of harvesting autogenous bone in other site. The method is simple and valuable to clinical application.

[Effects of yi-zhi II on synaptic structure of hippocampal CA3 and maintenance of memory].

AIM: To study the effects of yi-zhi II (a compond of Chinese Traditional Medicine) on the alteration of synaptic structure in hippocampal CA3 and maintenance of memoy. METHODS: By using the method of oral administration of yi-zhi II, the step-through test and electron microscopy, the latency of step-through and synaptic structure in hippocamal CA3 were tested. RESULTS: (1) The mice which had been given yi-zhi II prolong significantly the latency of step through (P < 0.05 or P < 0.01) on the 1st, 6th and 12th day after learning. (2) On the 6th and 12th day after learning, the length of synaptic active zone were markly improved in yi-zhi II and control, but that of yi-zhi II was better than that of control. (On the 6th day after learning, the number of perforated synapses and axo-dendrite synapses were significantly improved by the yi-zhi II (P < 0.05). CONCLUSION: The yi-zhi II could improve the learning and memory in mice. It migth improve the memory by increasing the length of synaptic active zone and the number of perforated synapses and axo-dendrite synapses in hippocampal CA3.