4‐tert‐butylcalix[4]arene (CA) is chemically incorporated into polymers of intrinsic microporosity (PIM‐1) via a one‐step nucleophilic copolymerization reaction to study the unprecedented synergistic effects of polymer structural tuning and the unique 3D cavity of CA on gas separation performance. From the wide‐angle X‐ray diffraction (XRD) and positron annihilation spectroscopy (PALS), two opposing structural effects of CA incorporation on polymer chains are found, with one being expansive for fractional free volume (FFV) and the other contractive. The bulky cup‐shape CA cavity reduces the chain packing efficiency, which increases FFV and the gas permeability, but the smaller dihedral angle of CA shrinks FFV, leading to the enhanced gas selectivity. More interestingly, CA's unique 3D open cavities also favor selective passage of gas molecules. These combinative effects impart PIM‐CA copolymer membranes with attractive and tunable gas transport properties. The gas permeability improves dominantly at small CA loadings while the selectivity is enhanced significantly at higher loadings, allowing PIM‐CA membranes with ≥1% CA loadings to perform beyond 2008 Robeson upper bounds for H2/N2, H2/CH4, CO2/N2, and CO2/CH4 separations. As a cheap commercial product with high chemical versatility, CA can expand the spectrum of PIM‐based membrane designs for more efficient hydrogen and natural gas purification processes.

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In spite of extensive observations and numerous theoretical studies in the past decades several key questions related with Gamma-Ray Bursts (GRB) emission mechanisms are still to be answered. Precise detection of the GRB polarization carried out by dedicated instruments can provide new data and be an ultimate tool to unveil their real nature. A novel space-borne Compton polarimeter POLAR onboard the Chinese space station TG2 is designed to measure linear polarization of gamma-rays arriving from GRB prompt emissions. POLAR uses plastics scintillator bars (PS) as gamma-ray detectors and multi-anode photomultipliers (MAPMTs) for readout of the scintillation light. Inherent properties of such detection systems are crosstalk and nonuniformity. The crosstalk smears recorded energy over multiple channels making both non-uniformity corrections and energy calibration more diffi- * Corresponding author.

The influences of optical fields on the group delay of chiral tunneling in graphene are investigated in real time using the finite-difference time-domain method. The group delay of tunneling electrons irradiated by an optical field is significantly different from that observed in traditional quantum tunneling. We found that when the barrier width increases, the group delay becomes constant for the reflected wave packet, but increases linearly for the transmitted wave packet. This peculiar tunneling effect can be attributed to current leakage in a time-dependent barrier generated via the optical Stark effect.Quantum tunneling time has received much attention since MacColl pointed out that it takes no approximate time ([1]; [2, 3] and references therein). The question of how long it takes an electron to tunnel through a potential barrier is still replete with controversy. The debates center around the definition of tunneling time and its exact physical meaning. Hartman [4] calculated the group delay or phase time and found that the group delay τ g becomes constant, while the barrier length increases. Thus, with a wider barrier, superluminal group velocities can be observed. Recently, Winful [3,5,6] proposed that the group delay in tunneling represents a lifetime of stored energy escaping through both sides of the barrier and does not represent a transit time. However, a unlimited group velocity is not a meaningful concept in tunneling and does not imply superluminality.

We investigate theoretically the light reflectance of a graphene layer prepared on the top of onedimensional Si/SiO2 photonic crystal (1DPC). It is shown that the visibility of the graphene layers is enhanced greatly when 1DPC is added, and the visibility can be tuned by changing the incident angle and light wavelengths. This phenomenon is caused by the absorption of the graphene layer and the enhanced reflectance of the 1DPC.PACS numbers: 78.40. Ri, 42.70.Qs, 42.79.Fm Graphene consists of a two-dimensional honeycomb lattice of carbon atoms and has been attracting attention recently due to its remarkable electronic properties and its potential application in nanoelectronics 1 . Graphene exhibits high crystal quality, an exotic Dirac-type spectrum, and ballistic transport on a submicro scale. Graphene samples are usually fabricated by a micromechnical cleavage of graphite. It is difficult to distinguish the single graphene layer from many graphitic pieces, even utilizing the atomic force, scanning-tunneling, and electron microscopes. A recent experiment demonstrated that the graphene visibility depends on both the thickness of the SiO 2 layer and the light wavelength 2 . They found that specific thicknesses (300nm and 100nm) are most suitable for its visual detection for the normal light incidence and attribute this phenomenon to the opacity of the graphene layer. Although the relative difference of the reflectance [the contrast C in Ref. (2)] is enhanced significantly, the absolute difference of the light reflectance is still quite low because it is determined by the weak absorption of the graphene layer. In order to enhance the visibility of graphene, i.e., the absolute and relative difference of the light reflectance of the graphene layer, we propose to prepare the graphene layer on the top of Si/SiO 2 one-dimensional photonic crystal(1DPC). This 1DPC shows a high dielectric contrast at the Si/SiO 2 interface (∆n ≈ 2.3) producing a high reflectance at normal incidence, and can be fabricated by different techniques, e.g., the separation-byimplantedoxygen technique 3 , sputtering 4 combined with solidsource Si molecular beam epitaxy 5 , and plasma-enhanced chemical vapor deposition 6 .In this Letter, we investigate theoretically the light reflectance of a graphene layer prepared on the top of Si/SiO 2 1DPC, as shown schematically in Fig. 1(a). We consider an asymmetric 1DPC: A 0 (AB) l , where l is an integer denoting the l -th layer. All layers are nonmagnetic (µ = 1) and are characterized by their permittivities ε A (SiO 2 layer), ε B (Si layer), and their thicknesses satisfywhere λ is the wavelength required by the observation. The thickness of the top SiO 2 layer is d = λ/2 √ ε A . We find that the differ- ence between the reflectance of the graphene layers with 1DPC can be enhanced greatly, even one order of magnitude larger than that without 1DPC. Furthermore, the visibility of the graphene can be tuned by the incident angle.We consider a light shedding on the graphene layer prepared on the top of Si/Si...