A high-flux beam of mass-filtered F+ at low energy (100-1300 eV) was scattered off Al and Si surfaces to study core-level excitations of F0 and F+. Elastic scattering behavior for F+ was observed at energies <300 (500) eV off Al (Si) for a 90 degrees lab angle. However, above this energy threshold, orbital mixing in the hard collision step results in electronic excitation of F via molecular orbital promotion along the 4f sigma (F-2p), significantly reducing the observed ion exit energy. In addition, despite the electronegativity of F, scattering at energies >450 (700) eV off Al (Si) produces F2+-behavior which is remarkably similar to Ne+ off the same surfaces. Inelasticities measured for single collision events agree well with the energy deficits required to form (doubly excited) F** and F+** states from F0 and F+, respectively; these excited species most likely decay to inelastic F+ and F2+ via autoionization.

We present a study on scattering of 100-1400 eV Ne + ions off Mg, Al, Si, and P surfaces. Exit energy distributions and yields of single-scattered Ne + and Ne 2+ were separately measured to investigate charge exchange mechanisms occurring at the onset of inelastic losses in binary hard collision events. At low incident energies, collisions appear elastic and projectile ion survival is dominated by nonlocal Auger-type neutralization involving the target valence band. However, once a critical R min ͑distance of closest approach͒ is reached, three phenomena occur simultaneously: Ne 2+ generation, reversal of the Ne + yield trend, and inelastic losses in Ne + and Ne 2+ . R min values for the Ne 2+ turn-on agree very well with the L-shell overlap distances of the colliding partners, suggesting that electron transfer involving the highly promoted 4f molecular orbital ͑correlated to the Ne 2p͒ at close internuclear distance ͑ϳ0.5 Å͒ is responsible. For the Ne + yield, a clear transition from nonlocal neutralization to R min -dependent collision induced neutralization was observed. Binary collision inelasticities ͑Q bin ͒ were evaluated for Ne + and Ne 2+ off Al and Si by taking into account electron straggling. Saturation-like behavior at R min Ͻ 0.5 Å was seen for Ne + ͑Q bin ϳ 40-45 eV͒ and Ne 2+ ͑68-75 eV͒. These losses fit well with double promotion of Ne 0 → Ne ** ͑2p 4 3s 2 , 41-45 eV͒ and Ne + → Ne +** ͑2p 3 3s 2 /3s3p, 69-72 eV͒, followed by autoionization as the projectile leaves the surface region to give Ne + and Ne 2+ . In contrast, Q bin values for Ne 2+ at the +2 turn-on were seen much lower ͑35-40 eV off Al, 55-60 eV off Si͒ than that required for double promotion-eliminating the possibility that Ne 2+ is only generated in double excitation of surviving Ne + . Thus single-electron excitation appears to be more important in the threshold region compared to the two-electron events seen at higher collision energies. In addition, the Ne + u P system shows striking similarities with the other target cases from the perspective of a well-defined Ne 2+ turn-on, continually increasing Ne 2+ yield with impact energy, and inelasticity values which point to the same 4f excitation pathway. The decreasing R min requirement for higher target Z in terms of Ne 2+ production has been confirmed for the Mg through P series, where hard collision excitation is governed by L-shell orbital overlaps.

A new iterative method for calculating energy levels and wave functionsThe exact transfer matrix approach used in studying sectionally constant potentials in one dimension is generalized to cylindrical and spherical geometries, where the potential depends only on radius. In each geometry two transfer matrices suffice to completely describe the wave function: one for handling a discontinuity in potential and one for handling a delta-function potential barrier. This method is then applied to the problem of confining a wave function in a cylindrical configuration using only a series of carefully placed delta function potential barriers. It is found that confinement can be made to increase nearly exponentially with the number of barriers if placed correctly, but that this arrangement has an exponentially sharp dependence on both barrier position and energy.

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Security is a core responsibility for Function-as-a-Service (FaaS) providers. The prevailing approach has each function execute in its own container to isolate concurrent executions of different functions. However, successive invocations of the same function commonly reuse the runtime state of a previous invocation in order to avoid container cold-start delays when invoking a function. Although efficient, this container reuse has security implications for functions that are invoked on behalf of differently privileged users or administrative domains: bugs in a function's implementation, third-party library, or the language runtime may leak private data from one invocation of the function to subsequent invocations of the same function.Groundhog isolates sequential invocations of a function by efficiently reverting to a clean state, free from any private data, after each invocation. The system exploits two properties of typical FaaS platforms: each container executes at most one function at a time and legitimate functions do not retain state across invocations. This enables Groundhog to efficiently snapshot and restore function state between invocations in a manner that is independent of the programming language/runtime and does not require any changes to existing functions, libraries, language runtimes, or OS kernels. We describe the design of Groundhog and its implementation in OpenWhisk, a popular production-grade open-source FaaS framework. On three existing benchmark suites, Groundhog isolates sequential invocations with modest overhead on end-to-end latency (median: 1.5%, 95p: 7%) and throughput (median: 2.5%, 95p: 49.6%), relative to an insecure baseline that reuses the container and runtime state.