Deterministic secure quantum communication with and without entanglement

We present a protocol for sending a message over a quantum channel with different layers of security that will prevent an eavesdropper from deciphering the message without being detected. The protocol has two versions where the bits are encoded in either pairs of entangled photons or separate photons. Unlike many other protocols, it requires a one-way, rather than a two-way, quantum channel and does not require a quantum memor. A quantum key is used to encrypt the message and both the key and the message are sent over the quantum channle with the same quantum encoding technique. The key is sent only if no eavesdropper is detected.Comment: 9 pages, 3 figures. Major changes in section 3 and 4. Accepted for publication in Physica Script

Study of Rock-Lining Interaction for Circular Tunnels Using Finite Element Analysis

Finite element technique is used to model two phases of tunneling process, namely; excavation and rocklining interaction. The excavation phase is responsible for determining the pre-lining rock mass deformations and the reduced in-situ stresses. The interaction phase models the compatibility of the rock-lining system. The deformations and stresses of the rock-lining system and the final rock mass pressure acting on the lining are determined. The finite element results are compared with the results of the Convergence-Confinement method for the case study (Shimizu Tunnel) that was guided by field measurements. One of the main objectives of this study is to investigate the effect of different parameters on the behavior of excavated tunnel before and after lining activation. The analysis followed the same procedure which had been applied in the analysis of the case of Shimizu Tunnel taking into consideration the different values of the tunnel radius and the depth of excavated tunnel through different qualities of rock ranging between poor, moderate and hard rock. The parametric study has been conducted for circular tunnel. The first lining system involved in this study was assumed to be shotcrete of thicknesses of 20, 30, 40 and 50cm, and the second lining system was steel ribs with shotcrete of thicknesses of 20, 30, 40 and 50cm. The results of Finite Element Analysis were presented for different thicknesses

Interpreting Recoil For Undergraduate Students

In this paper, I outline some problems in the students' understanding of the explanation of recoil motion when introduced to them in the context of Newton's third law. I propose to explain the origin of recoil from a microscopic point of view, which emphasizes the exact mechanism leading to recoil. This mechanism differs from one system to another. Several examples that can be easily implemented in the classroom environment are given in this paper. Such a profound understanding of the origin of recoil help students avoid some of the misconceptions that might arise from the phenomenological approach, and stimulates their thinking in the fundamental origins of other physical phenomena.Comment: To Appear in The Physics Teacher Magazin

The Potential of Hydrocyclone Application for Mammalian Cell Separation in Perfusion Cultivation Bioreactors

Hydrocyclones have been traditionally applied for long times in many industrial fields, such as in mineral processing and mining, chemical and petrochemical, and food industries. They have many characteristics that favor them as separation system in solid/liquid, gas/liquid and liquid/liquid processes. During the last two decades, they have been evaluated for their possible application in the separation of microbial and mammalian cells. Nowadays, mammalian cells are widely used for the production of a large number of valuable therapeutic proteins, antibodies, hormones and vaccines. This review highlights the potential of the application of hydrocyclones for mammalian cell separation in continuous perfusion biorecators. The discussion will cover the structure of hydrocyclone, mechanism of separation inside hydrocyclones, different theories describing the separation process, as well as the effect of changing different geometrical variables on the efficiency and performance of the separation process. Furthermore, we will focus on the latest developments achieved in the field of separation of living cells in both laboratory and pilot plant cultivation scales

Regression relation for pure quantum states and its implications for efficient computing

We obtain a modified version of the Onsager regression relation for the expectation values of quantum-mechanical operators in pure quantum states of isolated many-body quantum systems. We use the insights gained from this relation to show that high-temperature time correlation functions in many-body quantum systems can be controllably computed without complete diagonalization of the Hamiltonians, using instead the direct integration of the Schroedinger equation for randomly sampled pure states. This method is also applicable to quantum quenches and other situations describable by time-dependent many-body Hamiltonians. The method implies exponential reduction of the computer memory requirement in comparison with the complete diagonalization. We illustrate the method by numerically computing infinite-temperature correlation functions for translationally invariant Heisenberg chains of up to 29 spins 1/2. Thereby, we also test the spin diffusion hypothesis and find it in a satisfactory agreement with the numerical results. Both the derivation of the modified regression relation and the justification of the computational method are based on the notion of quantum typicality.Comment: 16 pages, 4 figures; minor textual corrections; parts rearrange