Spons & shields: practical isolation for trusted execution

Trusted execution environments (TEEs) promise a cost-effective, “lift-and-shift” solution for deploying security-sensitive applications in untrusted clouds. For this, they must support rich, multi-component applications, but a large trusted computing base (TCB) inside the TEE risks that attackers can compromise application security. Fine-grained compartmentalisation can increase security through defense-in-depth, but current solutions either run all software components unprotected in the same TEE, lack efficient shared memory support, or isolate application processes using separate TEEs, impacting performance and compatibility. We describe the Spons & Shields framework (SSF) for Intel SGX TEEs, which offers intra-TEE compartmentalisation using two new abstraction, Spons and Shields. Spons and Shields generalise process, library and user/kernel isolation inside the TEE while allowing for efficient memory sharing. When users deploy unmodified multi-component applications in a TEE, SSF dynamically creates Spons (one per POSIX process or library) and Shields (to enforce a given security policy for memory accesses). Applications can be hardened with minor code changes, e.g., by using a separate Shield to isolate an SSL library. SSF uses compiler instrumentation to protect Shield boundaries, exploiting MPX instructions if available. We evaluate SSF using a complex application service (NGINX, PHP interpreter and PostgreSQL) and show that its overhead is comparable to process isolation

Sensitivity of nonlinear photoionization to resonance substructure in collective excitation

Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pave the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources

EUV ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization and electron energy-loss spectra

The ionization dynamics of pure He nanodroplets irradiated by EUV radiation is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence (VMI-PEPICO) spectroscopy. We present photoelectron energy spectra and angular distributions measured in coincidence with the most abundant ions He+, He2+, and He3+. Surprisingly, below the autoionization threshold of He droplets we find indications for multiple excitation and subsequent ionization of the droplets by a Penning-like process. At high photon energies we evidence inelastic collisions of photoelectrons with the surrounding He atoms in the droplets

Education for collaboration: the influence of the third space on professional boundaries

The delivery of integrated care requires the establishment of effective professional relationships that foster collaborative working across health systems. Evidence for how to prepare practitioners to work in those settings is limited. By exploring an innovative postgraduate Programme for Integrated Child Health (PICH) this article highlights the conditions by which effective collaboration can be encouraged. Our qualitative evaluation of PICH involved one-to-one semi-structured interviews with 23 postgraduate general practice and paediatric trainees and their mentors. We analysed the data using the concept of the ‘third space’, where multiple discourses between individuals with diverse professional backgrounds occur, enabling creative exploration of tensions inherent in new ways of working in order to identify enablers and barriers to collaboration. Our analysis identified three themes that enabled collaboration: effective communication, boundary work and educational spaces; and four themes that were barriers: traditional hierarchical professional identities, curriculum design, financial systems and workplace spaces. PICH demonstrated the value of educational spaces and their role in enabling collaborative practice, as participants explored their professional identities and those of other disciplines. Structural factors in the workplace which inhibit collaborative practice were also evident. We conclude by proposing a model for collaborative learning in third spaces based upon the recognition that, while educational programmes alone will not lead to change, they have the potential to inform the development of productive workplace spaces that will be required if collaborative practice in healthcare is to become a reality

Structural stability of Fe5Si3 and Ni2Si studied by high-pressure x-ray diffraction and ab initio total-energy calculations

We performed high-pressure angle dispersive x-ray diffraction measurements on Fe5Si3 and Ni2Si up to 75 GPa. Both materials were synthesized in bulk quantities via a solid-state reaction. In the pressure range covered by the experiments, no evidence of the occurrence of phase transitions was observed. On top of that, Fe5Si3 was found to compress isotropically, whereas an anisotropic compression was observed in Ni2Si. The linear incompressibility of Ni2Si along the c-axis is similar in magnitude to the linear incompressibility of diamond. This fact is related to the higher valence-electron charge density of Ni2Si along the c-axis. The observed anisotropic compression of Ni2Si is also related to the layered structure of Ni2Si where hexagonal layers of Ni2+ cations alternate with graphite-like layers formed by (NiSi)2- entities. The experimental results are supported by ab initio total-energy calculations carried out using density functional theory and the pseudopotential method. For Fe5Si3, the calculations also predicted a phase transition at 283 GPa from the hexagonal P63/mcm phase to the cubic structure adopted by Fe and Si in the garnet Fe5Si3O12. The room-temperature equations of state for Fe5Si3 and Ni2Si are also reported and a possible correlation between the bulk modulus of iron silicides and the coordination number of their minority element is discussed. Finally, we report novel descriptions of these structures, in particular of the predicted high-pressure phase of Fe5Si3 (the cation subarray in the garnet Fe5Si3O12), which can be derived from spinel Fe2SiO4 (Fe6Si3O12).Comment: 44 pages, 13 figures, 3 Table

Transformation Pathways of Silica under High Pressure

Concurrent molecular dynamics simulations and ab initio calculations show that densification of silica under pressure follows a ubiquitous two-stage mechanism. First, anions form a close-packed sub-lattice, governed by the strong repulsion between them. Next, cations redistribute onto the interstices. In cristobalite silica, the first stage is manifest by the formation of a metastable phase, which was observed experimentally a decade ago, but never indexed due to ambiguous diffraction patterns. Our simulations conclusively reveal its structure and its role in the densification of silica.Comment: 14 pages, 4 figure

The South West Clinical School model: an initiative to transform clinical academic career pathways

Background: The Clinical School Model connects professorial staff from the university directly to practitioners in the National Health Service to promote evidence informed practice and develop clinical academic careers. These are promoted widely, but strategic adoption into organisational culture and workforce plans are challenging to overcome. Aims: To describe the development of the Clinical School Model in Cornwall and explore how it generates impact through staff engagement activities to support clinical academic career pathways. Structure, process and outcomes developments over the last 3-years are reported. Methods: Donabedian’s framework (structure, process and outcome) was used to report on the development and impact of the Clinical School Model. Results: Structural and process activities are reported, illustrating strong foundations to embed clinical academic career pathway opportunities. In the absence of empirical reporting standards for such developments, quantitative and qualitative outcomes are reported against the Clinical School’s 5-year strategic plan. Conclusions: This paper responds to the lack of reported evidence on developing organisational infrastructure to address the clinical academics aspirations of nurses and their employers. This important contribution leads a call for more organisations to report to the evidence base, enabling shared learning and shaping future research. </jats:sec

The calibration of the Sudbury Neutrino Observatory using uniformly distributed radioactive sources

The production and analysis of distributed sources of 24Na and 222Rn in the Sudbury Neutrino Observatory (SNO) are described. These unique sources provided accurate calibrations of the response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy betas and gammas. The application of these sources in determining the neutron detection efficiency and response of the 3He proportional counter array, and the characteristics of background Cherenkov light from trace amounts of natural radioactivity is described.Comment: 24 pages, 13 figure

Photoelectron Angular Distributions for Two-photon Ionization of Helium by Ultrashort Extreme Ultraviolet Free Electron Laser Pulses

Phase-shift differences and amplitude ratios of the outgoing $s$ and $d$ continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.Comment: 5 pages, 1 table, 3 figure