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The internal inhomogeneous deformation and re-breaking characteristics of broken rock and coal during compaction are the basis for understanding porous structure evolution of the caved zone and then affect the enrichment of coalbed methane (CBM) in mining gob. In this paper, compression-AE experiments on limestone are carried out using a self-developed AE testing system. An AE location method, which is especially suitable for broken porous media is proposed. The results show that 1) the compression process of broken limestone can be divided into three stages: initial compression, linear compression, and plastic compression. There is a good correspondence between AE counts, energy and compression stages. 2) Broken limestone has layered re-breaking characteristics: the particle re-breaking firstly occurs in the middle layer and gradually moves toward the upper and lower layers as compression degree increases. The ultimate re-breaking degree in upper and middle layers is larger than that in lower layer. 3) The final screened results when strain rate reaches 0.24 show that the reduction of porosity is larger in upper and middle layers than that in lower layer under loading. The lower layer owns the largest porosity due to relative smaller compression degree.

Hydroxylatopillar[6]arene (HP6) has been used as a stable ligand for the synthesis of gold nanoparticles (AuNPs). HP6 with excellent molecular recognition capability will securely capture the elect...

This study focuses on the stability of stone column-supported and geosynthetic-reinforced embankments on soft soil. An upper-bound limit state plasticity failure discretization scheme (known as discontinuity layout optimization (DLO)), which determines the embankment stability without pre-assuming a slip surface, is used. The relationships between the stability of stone column-supported and geosynthetic-reinforced embankments and various influencing parameters, including the soil strength, geometric configuration, reinforcement strength, and area replacement ratio, are analysed. It is found that geosynthetics provide a significant contribution to embankment stability. Two failure mechanisms of geosynthetics (i.e., rupture failure and bond failure) are revealed and the effect of geosynthetics on embankment stability is governed by the failure mode. The application of stone columns mitigates the risk of geosynthetic failure. To provide an analytical solution for primary design in engineering practice, an approach based on the limit equilibrium method is proposed. Validations are performed with the DLO solution to demonstrate the accuracy and reliability of the developed analytical approach.

Excavations may cause excessive ground movements, resulting in potential damage to laterally adjacent tunnels. The aim of this investigation is to present a simple assessment technique using a multivariate adaptive regression splines (MARS) model, which can map the nonlinear interactions between the influencing factors and the maximum horizontal deformation of tunnels. A high-quality case history in Tianjin, China, is presented to illustrate the effect of excavation on the tunnel deformation and to validate the FEM. The hypothetical data produced by the FEM provide a basis for developing the proposed MARS model. Based on the proposed model, the independent and coupled effects of the input variables (i.e. the normalized buried depth of tunnels Ht/He, the normalized horizontal distance between tunnels and retaining structures Lt/He, and the maximum horizontal displacement of retaining structures, δRmax) on the tunnel response are analysed. The prediction precision and accuracy of the MARS model are validated via the artificial data and the collected case histories.

Coherent terahertz (THz) wave emission from indium tin oxide (ITO) in epsilon-near-zero region had been reported recently as a second-order nonlinear process. However, THz radiation from ITO through third-order nonlinear process has not been reported yet. Here, we demonstrate coherent THz radiation from an ITO film via four-wave mixing, a third-order nonlinear process, under the excitation of two-color pulsed laser fields. Experimentally, an in-line phase compensator is utilized to synthesize the asymmetric optical fields to induce photocurrent in an ITO film and consequently emit THz waves. Our experimental results show that THz radiation from ITO films can be coherently controlled by the relative phase between the two-color laser fields. Such a THz wave generation process can be attributed to the fast intra-band nonlinearity in the conduction band. Our demonstration reveals that the fast nonlinearity in ITO can be used to generate THz waves and promotes the investigation of ITO in ultrafast photonics.

In this paper, the bearing capacity and the failure mechanism of obliquely loaded footings on sand overlying clay are determined by using discontinuity layout optimization (DLO) procedure. The solution is illustrated as a set of design charts with the use of dimensionless parameters. Parametric studies are performed to show that soil properties, geometric parameters, and load inclinations are all related to the bearing capacity and failure pattern. A simplified model is developed based on artificial data generated through DLO. Validations are carried out to demonstrate the accuracy of the developed model.

The gamma-aminobutyric acid type B (GABAB) receptor may participate in the development of diabetic neuropathic pain (DNP). BHF177 serves as a positive allosteric modulator of the GABAB receptor. In the current study, we sought to study the role of the BHF177-GABAB receptor in DNP and its underlying mechanism. Streptozotocin was adopted to induce a rat model of DNP, followed by determination of the paw withdrawal threshold (PWT), paw withdrawal latency (PWL), and glucose level. The effect of BHF177 on DNP by regulating the GABAB receptor in vivo was determined by the injection of BHF177 and/or CGP46381 (a GABAB receptor antagonist) into rat models of DNP. Hippocampal neuronal cells were isolated and cultured, and the neurons and DNP model rats were treated with activators of PKC (PMA), CaMKII (CaCl2), or ERK1/2 (EGF) to study the role of GABAB receptors in DNP via regulation of the NR2B-PKC-CaMKII-ERK-CREB pathway. BHF177 suppressed DNP symptoms by activating the GABAB receptors, as evidenced by increased PWT and PWL of DNP rats and the increased number of neurons expressing the GABAB receptor, but this effect was reversed by CGP46381 treatment. BHF177 treatment markedly repressed PKC, CaMKII, p-ERK1/2, and p-CREB expressions in the rat DNP model, but these suppressive effects were abrogated by treatments with PMA, CaCl2, or EGF treatment, respectively. To sum up, BHF177 suppresses DNP symptoms by blocking the PKC/CaMKII/ERK1/2/CREB signaling pathway to activate the GABAB receptors.

The large number of spatial modes supported by standard multimode fibers is a promising platform for boosting the channel capacity of quantum and classical communications by orders of magnitude. However, the practical use of long multimode fibers is severely hampered by modal crosstalk and polarization mixing. To overcome these challenges, we develop and experimentally demonstrate a vectorial time reversal technique, which is accomplished by digitally pre-shaping the wavefront and polarization of the forward-propagating signal beam to be the phase conjugate of an auxiliary, backward-propagating probe beam. Here, we report an average modal fidelity above 80% for 210 Laguerre-Gauss and Hermite-Gauss modes by using vectorial time reversal over an unstabilized 1-km-long fiber. We also propose a practical and scalable spatial-mode-multiplexed quantum communication protocol over long multimode fibers to illustrate potential applications that can be enabled by our technique., Comment: Supplementary Information is included

Quantum-state tomography is the conventional method used to characterize density matrices for general quantum states. However, the data acquisition time generally scales linearly with the dimension of the Hilbert space, hindering the possibility of dynamic monitoring of a high-dimensional quantum system. Here, we demonstrate a direct tomography protocol to measure density matrices of photons in the position basis through the use of a polarization-resolving camera, where the dimension of density matrices can be as large as $580\ifmmode\times\else\texttimes\fi{}580$ in our experiment. The use of the polarization-resolving camera enables parallel measurements in the position and polarization basis and as a result, the data acquisition time of our protocol does not increase with the dimension of the Hilbert space and is solely determined by the camera exposure time (on the order of 10 ms). Our method is potentially useful for the real-time monitoring of the dynamics of quantum states and paves the way for the development of high-dimensional, time-efficient quantum metrology techniques.

We demonstrate that digital multi-probe time reversal can effectively suppress crosstalk for mode-division multiplexing. The performance of multi-probe time reversal is experimentally characterized over a 340-m free-space link and a 1-km standard multimode fiber.

We propose and demonstrate a single-pixel temporal imaging system with high resolution, efficiency and sensitivity. A terahertz pulse with pulse energy as low as 5 fJ is compressively imaged with a resolution down to 16 fs.

Using computational algorithms to measure terahertz (THz) fields has been studied in the past decade. We develop a flexible and robust technique based on probe beam encoding. Our new approach does not require any additional manufacture, ancillary semiconductors or nanofilms. By imaging in the near-field, we can recover the THz field with 62 μ $m$ resolution, which is 15 times smaller than the central wavelength (940 μm).

The orbital angular momentum (OAM) of photons presents a degree of freedom for enhancing the secure key rate of free-space quantum key distribution (QKD) through mode-division multiplexing (MDM). However, atmospheric turbulence can lead to substantial modal crosstalk, which is a long-standing challenge to MDM for free-space QKD. Here, we show that the digital generation of time-reversed wavefronts for multiple probe beams is an effective method for mitigating atmospheric turbulence. We experimentally characterize seven OAM modes after propagation through a 340-m outdoor free-space link and observe an average modal crosstalk as low as 13.2% by implementing real-time time reversal. The crosstalk can be further reduced to 3.4% when adopting a mode spacing $\Delta \ell$ of 2. We implement a classical MDM system as a proof-of-principle demonstration, and the bit error rate is reduced from $3.6\times 10^{-3}$ to be less than $1.3\times 10^{-7}$ through the use of time reversal. We also propose a practical and scalable scheme for high-speed, mode-multiplexed QKD through a turbulent link. The modal crosstalk can be further reduced by using faster equipment. Our method can be useful to various free-space applications that require crosstalk suppression., Comment: Supplemental Material is included

In this technical note, the seismic bearing capacity coefficients of shallow foundations placed on soft ground reinforced by stone columns are evaluated based on the upper-bound theorem of...

We propose a practical high-dimensional quantum key distribution protocol based on mutually partially unbiased bases utilizing transverse modes of light. In contrast to conventional protocols using mutually unbiased bases, our protocol uses Laguerre-Gaussian and Hermite-Gaussian modes of the same mode order as two mutually partially unbiased bases for encoding, which leads to a scheme free from mode-dependent diffraction in long-distance channels. Since only linear and passive optical elements are needed, our experimental implementation significantly simplifies qudit generation and state measurement. Since this protocol differs from conventional protocols using mutually unbiased bases, we provide a security analysis of our protocol.

The orbital angular momentum (OAM) of photons is a promising degree of freedom for high-dimensional quantum key distribution (QKD). Due to the greater flexibility in applications and the lower loss, QAM QKD over the free-space channel is still significant. However, effectively mitigating the adverse effects of atmospheric turbulence is a persistent challenge. In contrast to previous works focusing on correcting static simulated turbulence, we investigate the performance of OAM QKD in real atmospheric turbulence with real-time adaptive optics (AO) correction. We show that, it is possible to mitigate the errors induced by weak turbulence and establish a secure channel under some conditions. The cross-talk induced by turbulence and the performance of AO systems are investigated in a lab-scale link with controllable turbulence. The relations between the crosstalk and AO specifications is also studied. Our experimental results suggest that an advanced AO system with fine beam tracking, reliable beam stabilization, precise wavefront sensing and accurate wavefront correction is necessary to adequately correct turbulence-induced error.

Computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators, or complicated systems requiring assistance from photon-excited free-carriers with high-speed synchronization among multiple optical beams. Here, by spatially encoding an 800 nm near-infrared (NIR) probe beam through the use of an optical SLM, we demonstrate a simple sampling approach that can probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. By using computational algorithms, we successfully measure 128×128 field distributions with a 62 μm transverse spatial resolution, more than 15 times smaller than the central wavelength of the THz signal (940 μm. Benefiting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws in industrial products, and so on.

In contrast to imaging using position-resolving cameras, single-pixel imaging uses a bucket detector along with spatially structured illumination to compressively recover images. This emerging imaging technique is a promising candidate for a broad range of applications due to the high signal-to-noise ratio (SNR) and sensitivity, and applicability in a wide range of frequency bands. Here, inspired by single-pixel imaging in the spatial domain, we demonstrate a time-domain single-pixel imaging (TSPI) system that covers frequency bands including both terahertz (THz) and near-infrared (NIR) regions. By implementing a programmable temporal fan-out gate based on a digital micromirror device, we can deterministically prepare temporally structured pulses with a temporal sampling size down to 16.00 ± 0.01 f s . By inheriting the advantages of detection efficiency and sensitivity from spatial single-pixel imaging, TSPI enables the recovery of a 5 fJ THz pulse and two NIR pulses with over 97 % fidelity via compressive sensing. We demonstrate that the TSPI is robust against temporal distortions in the probe pulse train as well. As a direct application, we apply TSPI to machine-learning-aided THz spectroscopy and demonstrate a high sample identification accuracy (97.5%) even under low SNRs (SNR ∼ 10 ).

Polarization and spatial mode cross-talk limit the usability of multimode fibers for data transfer. We implement vectorial phase conjugation to transmit modes through standard multimode fiber with an average fidelity of 84.1% for 210 modes.

We explore the use of a switchable single-photon detector (SPD) array scheme to reduce the effect of a detector’s deadtime for a multi-bit/photon quantum link. The case of data encoding using M possible orbital-angular-momentum (OAM) states is specifically studied in this paper. Our method uses N SPDs with a controllable M × N optical switch and we use a Monte Carlo-based method to simulate the quantum detection process. The simulation results show that with the use of the switchable SPD array, the detection system can allow a higher incident photon rate than what might otherwise be limited by detectors’ deadtime. For the case of M = 4 , N = 20 , a 50-ns deadtime for the individual SPDs, an average photon number per pulse of 0.1, and under the limit that at most 10 % of the photon-containing pulses are missed, the switchable SPD array will allow an incident photon rate of 2250 million counts/s (Mcts/s). This is 25 times the 90 Mcts/s incident photon rate that a non-switchable, 4-SPD array will allow. The increase in incident photon rate is more than the 5 times increase, which is the simple increase in the number of SPDs and the number of OAM encoding states (e.g., N ∕ M = 20 ∕ 4 ).

The dimension of the state space for information encoding offered by the transverse structure of light is usually limited by the finite size of apertures. The widely used orbital angular momentum (OAM) number of Laguerre-Gaussian (LG) modes in free-space communications cannot achieve the theoretical maximum transmission capacity unless the radial degree of freedom is multiplexed into the protocol. While the methodology to sort the radial quantum number has been developed, the application of radial modes in quantum communications requires an additional ability to efficiently measure the superposition of LG modes in the mutually unbiased basis. Here we develop and implement a generic mode sorter that is capable of sorting the superposition of LG modes through the use of a mode converter. As a consequence, we demonstrate an 8-dimensional quantum key distribution experiment involving all three transverse degrees of freedom: spin, azimuthal, and radial quantum numbers of photons. Our protocol presents an important step towards the goal of reaching the capacity limit of a free-space link and can be useful to other applications that involve spatial modes of photons.