Quantum key distribution based on arbitrarily weak distillable entangled states

States with private correlations but little or no distillable entanglement were recently reported. Here, we consider the secure distribution of such states, i.e., the situation when an adversary gives two parties such states and they have to verify privacy. We present a protocol which enables the parties to extract from such untrusted states an arbitrarily long and secure key, even though the amount of distillable entanglement of the untrusted states can be arbitrarily small.     

Ab initio rigid water: effect on water structure, ion hydration, and thermodynamics

We investigate the liquid structure, ion hydration, and some thermodynamic properties associated with the rigid geometry approximation to water by applying ab initio molecular dynamics simulations (AIMD) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional at T = 320 K. We vary the rigid water geometry in order to locate a class of practical water models that yield reasonable liquid structure and dynamics, and to examine the progression of AIMD-predicted water behavior as the OH bond length varies. Water constrained at the optimal PBE gas phase geometry yields reasonable pair correlation functions. The predicted liquid phase pressure, however, is large ( approximately 8.0 kbar). Although the O-H bond in water should elongate when transferred from gas to the condensed phase, when it is constrained to 0.02, or even just 0.01 A longer than the optimal gas phase value, liquid water is predicted to be substantially overstructured compared to experiments. Zero temperature calculations of the thermodynamic properties of cubic ice underscore the sensitivity toward small variations in the O-H bond length. We examine the hydration structures of potassium, chloride, and formate ions in one rigid PBE water model. The results are in reasonable agreement with unconstrained AIMD simulations.     

Construction of a pH-driven supramolecular nanovalve

[Structure: see text] The versatility of supramolecular chemistry has been exploited in constructing nanovalves based on mesoporous silica MCM-41 and the mutual recognition between secondary dialkylammonium ions and dibenzo[24]crown-8 (DB24C8). Naphthalene-containing dialkylammonium threads were tethered to the MCM-41, followed by loading with coumarin 460 and capping with DB24C8. Controlled release of coumarin 460 from the pores of MCM-41 was demonstrated using different bases. The rate of release of coumarin 460 from the nanovalves depends on the size of the base.     

Effects on the polarizability of mesoscopic metallic nanoparticles

The effects of temperature variation on the electric polarizability of mesoscopic metallic nanoparticles is studied via a theoretical model in which the temperature dependence of the electron–phonon and electron–electron scattering rates are taken into account. Furthermore, the nonlocal response of the metal, which is significant for particles of mesoscopic dimensions, is also included. It is found that the significance of the nonlocal effects can be very different with different metals, for the same smallness in size of the nanoparticles. In addition, while the imaginary part of the polarizability in general increases with temperature, the real part can both decrease or increase as temperature rises—in contrast to the case with the static polarizability of atomic clusters, which most of the time increases with temperature.     

Relative reactivities of amino and ethenyl groups in allylamine on Si(100)2 × 1: Temperature-dependent X-ray photoemission and thermal desorption studies of a common linker molecule

The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1 s feature at 398.9 eV, attributed to a N―Si bond, indicates N―H dissociative adsorption. On the other hand, the presence of C 1 s features at 284.6 eV and 286.2 eV, corresponding to C═C and C―N, respectively, and the absence of the Si―C feature expected at 283.2 eV shows that [2 + 2] C═C cycloaddition does not occur at room temperature. These XPS data are consistent with the unidentate staggered and eclipsed allylamine conformer adstructures arising from N―H dissociation and not [2 + 2] C═C cycloaddition. The apparent conversion of the N 1 s feature for Si―N(H)―C

at 398.9 eV to that for Si―N(H) at 397.7 eV and the total depletion of C 1 s feature for C―N at 286.2 eV near 740 K indicates cleavage of the C―N bond, leaving behind a Si―N(H) radical. Furthermore, the C═C C 1 s feature at 284.6 eV undergoes steep intensity reduction between 740 K and 825 K, above which a new C 1 s feature at 283.2 eV corresponding to SiC is found to emerge. These spectral changes suggest total dissociation of the ethenyl fragment and the formation of SiC. Moreover, while the total N 1 s intensity undergoes a minor reduction (24%) upon annealing up to 1090 K, a considerable reduction (43%) is found in the overall C 1 s intensity. This observation is consistent with our TDS data, which shows the desorption of C-containing molecules including propene and ethylene at 580 K and of acetylene at 700 K. The lack of N-containing desorbates suggests that the dissociated N species are likely bonded to multiple surface Si atoms or diffused into the bulk. Interestingly, both the staggered and eclipsed N―H dissociative adstructures are found to have a less negative adsorption energy than the [N, C, C] tridentate or the [2 + 2] C═C cycloaddition adstructures by our DFT calculations, which suggests that the observed formation of N―H dissociative adstructures is kinetically favored on the Si(100)2 × 1 surface.     

Flexible sliced designs for computer experiments

Sliced Latin hypercube designs are popularly adopted for computer experiments with qualitative factors. Previous constructions require the sizes of different slices to be identical. Here we construct sliced designs with flexible sizes of slices. Besides achieving desirable one-dimensional uniformity, flexible sliced designs (FSDs) constructed in this paper accommodate arbitrary sizes for different slices and cover ordinary sliced Latin hypercube designs as special cases. The sampling properties of FSDs are derived and a central limit theorem is established. It shows that any linear combination of the sample means from different models on slices follows an asymptotic normal distribution. Some simulations compare FSDs with other sliced designs in collective evaluations of multiple computer models.     

Scheduling two agents with controllable processing times

We consider several two-agent scheduling problems with controllable job processing times, where agents A and B have to share either a single machine or two identical machines in parallel while processing their jobs. The processing times of the jobs of agent A are compressible at additional cost. The objective function for agent B is always the same, namely a regular function _fmax$f_{\text{max}}$. Several different objective functions are considered for agent A, including the total completion time plus compression cost, the maximum tardiness plus compression cost, the maximum lateness plus compression cost and the total compression cost subject to deadline constraints (the imprecise computation model). All problems are to minimize the objective function of agent A subject to a given upper bound on the objective function of agent B. These problems have various applications in computer systems as well as in operations management. We provide NP-hardness proofs for the more general problems and polynomial-time algorithms for several special cases of the problems.     

On Lander’s conjecture for difference sets whose order is a power of 2 or 3

Let p be a prime and let b be a positive integer. If a (v, k, λ, n) difference set D of order n = p ^b exists in an abelian group with cyclic Sylow p-subgroup S, then \({p\in\{2,3\}}\) and |S| = p. Furthermore, either p = 2 and v ≡ λ ≡ 2 (mod 4) or the parameters of D belong to one of four families explicitly determined in our main theorem.     

Defects in ZnO nanorods prepared by a hydrothermal method

ZnO nanorod arrays were fabricated using a hydrothermal method. The nanorods were studied by scanning electron microscopy, photoluminescence (PL), time-resolved PL, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy before and after annealing in different environments and at different temperatures. Annealing atmosphere and temperature had significant effects on the PL spectrum, while in all cases the positron diffusion length and PL decay times were increased. We found that, while the defect emission can be significantly reduced by annealing at 200 degrees C, the rods still have large defect concentrations as confirmed by their low positron diffusion length and short PL decay time constants.