Holographic data storage in a DX-center material

We report on the optical storage of digital data in a semiconductor sample containing DX centers. The diffraction efficiency and the bit-error-rate performance of multiplexed data images are shown to agree well with a simple model of the material. Uniform storage without an exposure schedule is demonstrated. The volume sensitivity is found to be ~10^3 times that of LiNBO3:Fe. The importance of coherent addition of scattered light with diffracted light in holographic data storage is discussed

Storage Density of Shift-Multiplexed Holographic Memory

The storage density of shift-multiplexed holographic memory is calculated and compared with experimentally achieved densities by use of photorefractive and write-once materials. We consider holographic selectivity as well as the recording material s dynamic range (M /#) and required diffraction efficiencies in formulating the calculations of storage densities, thereby taking into account all major factors limiting the raw storage density achievable with shift-multiplexed holographic storage systems. We show that the M /# is the key factor in limiting storage densities rather than the recording material s thickness for organic materials in which the scatter is relatively high. A storage density of 100 bits m2 is experimentally demonstrated by use of a 1-mm-thick LiNbO3 crystal as the recording medium

Electromagnetic energy storage and power dissipation in nanostructures

The processes of storage and dissipation of electromagnetic energy in nanostructures depend on both the material properties and the geometry. In this paper, the distributions of local energy density and power dissipation in nanogratings are investigated using the rigorous coupled-wave analysis. It is demonstrated that the enhancement of absorption is accompanied by the enhancement of energy storage both for material at the resonance of its dielectric function described by the classical Lorentz oscillator and for nanostructures at the resonance induced by its geometric arrangement. The appearance of strong local electric field in nanogratings at the geometry-induced resonance is directly related to the maximum electric energy storage. Analysis of the local energy storage and dissipation can also help gain a better understanding of the global energy storage and dissipation in nanostructures for photovoltaic and heat transfer applications

H4-Alkanes: A new class of hydrogen storage material?

The methane-based material (H$_2$)$_4$CH$_4$, also called H4M for short, is in essence a methane molecule with 4 physisorbed H$_2$ molecules. While H4M has exceptionally high hydrogen storage densities when it forms a molecular solid, unfortunately, this solid is only stable at impractically high pressures and/or low temperatures. To overcome this limitation, we show through simulations that longer alkanes (methane is the shortest alkane) also form stable structures that still physisorb 4 H$_2$ molecules per carbon atom; we call those structures H4-alkanes. We further show via molecular dynamics simulations that the stability field of molecular solids formed from H4-alkanes increases remarkably with chain length compared to H4M, just as it does for regular alkanes. From our simulations of H4-alkanes with lengths 1, 4, 10, and 20, we see that e.g. for the 20-carbon the stability field is doubled at higher pressures. While even longer chains show only insignificant improvements, we discuss various other options to stabilize H4-alkanes more. Our proof-of-principle results lay the groundwork to show that H4-alkanes can become viable hydrogen storage materials.Comment: 6 pages, 7 figure

Graphene Oxide as an Optimal Candidate Material for Methane Storage

Methane, the primary constituent of natural gas, binds too weakly to nanostructured carbons to meet the targets set for on-board vehicular storage to be viable. We show, using density functional theory calculations, that replacing graphene by graphene oxide increases the adsorption energy of methane by 50%. This enhancement is sufficient to achieve the optimal binding strength. In order to gain insight into the sources of this increased binding, that could also be used to formulate design principles for novel storage materials, we consider a sequence of model systems, that progressively take us from graphene to graphene oxide. A careful analysis of the various contributions to the weak binding between the methane molecule and the graphene oxide shows that the enhancement has important contributions from London dispersion interactions as well as Debye interactions and higher-order electrostatic interactions, aided by geometric curvature induced primarily by the presence of epoxy groups.Comment: 12 pages, 19 figure

Numerical Study on Transient Heat Characteristics of a Rectangular Latent Heat Storage Vessel

Transient characteristics of the rectangular latent heat storage vessel packed with shape-stabilized phase change (solid-liquid) material (PCM) are investigated numerically by solving the governing equations of both the PCM and the heat transfer medium(water) simultaneously as a conjugate problem with the finite difference technique. It's found that the heat storage characteristics are greatly affected by the flow direction of the heat transfer medium since the natural and forced convection coexists in the heat storage vessel. That is, it is classified that the effectively thermal efficiency of the latent heat storage system is obtained by the downflow along vertical PCM for heat storage process and the upflow for heat release process. The effect of the inlet velocity of heat transfer medium(water) on transient heat characteristics of the latent heat storage system is also revealed in the present study

Storage and Retrieval of a Microwave Field in a Spin Ensemble

We report the storage and retrieval of a small microwave field from a superconducting resonator into collective excitations of a spin ensemble. The spins are nitrogen-vacancy centers in a diamond crystal. The storage time of the order of 30 ns is limited by inhomogeneous broadening of the spin ensemble.Comment: 4 pages + supplementary material. Submitted to PR

Cryogenic container compound suspension strap

A support strap for use in a cryogenic storage vessel for supporting the inner shell from the outer shell with a minimum heat leak is presented. The compound suspension strap is made from a unidirectional fiberglass epoxy composite material with an ultimate tensile strength and fatigue strength which are approximately doubled when the material is cooled to a cryogenic temperature

Modelling of high temperature storage systems for latent heat

There is a huge demand for heat storages for evaporation applications. Thermal storage systems are used to increase the efficiency of thermal systems by an improved adaption of energy availability and energy demand. In this paper a possible solution for modular storage systems from 200-600 °C and pressures up to 100 bar is presented. The application of steam as a working medium requires the availability of isothermal storage if charging/discharging should take place at almost constant pressure. The saturation temperature range is between 200°C and 320°C. Therefore nitrate salts are used as phase change material (PCM). The solution developed at DLR is characterized by a modular concept of tube register storages surrounded by both sensible and latent heat storage material. The focus in this paper is on modelling of the PCM storage. A model is introduced for melting and freezing of the PCM. To perform with an acceptable heat transfer rate inside the PCM, fins are used to increase the overall thermal conductivity. Instead introducing mean storage material parameters, like thermal conductivity or specific heat capacity, the geometry of the finned tube is modelled by using discrete elements. Therefore the model allows detailed studies on heat transfer during space and time. The fin design can be varied in order to find an optimal configuration. A set of partial differential equations is created and solved. When considering a stand alone system, that means tube, fin and PCM, without a connection to other components, investigation is quite effective. In case of the PCM storage there is the big advantage, compared with a sensible regenerator, that the almost constant fluid temperature, when evaporating or condensing, leads to a uniform temperature distribution in fluid flow direction. Therefore only a very rough discretisation in axial direction is needed, what even allows bonding with other components e.g. from the Modelica Fluid Library. Sensible storages as they are used for preheating and superheating have a characteristic temperature gradient in axial direction. To describe their thermal behaviour concentrated models, using dimensionless numbers, are used

Apparatus for recovering matter adhered to a host surface

The development of an apparatus for removing and recovering matter adhered to a host surface is described. The device consists of a pickup head with an ultrasonic transducer adapted to deliver ultrasonic pressure waves against the material. The ultrasonic waves agitate the material and cause its separation from the surface. A vacuum system recovers the material and delivers it to suitable storage containers