The design and evaluation of grazing incidence relay optics

X-ray astronomy, both solar and celestial, has many needs for high spatial resolution observations which have to be performed with electronic detectors. If the resolution is not to be detector limited, plate scales in excess of 25 microns arc/sec, corresponding to focal lengths greater than 5 m, are required. In situations where the physical size is restricted, the problem can be solved by the use of grazing incidence relay optics. A system was developed which employs externally polished hyperboloid-hyperboloid surfaces to be used in conjunction with a Wolter-Schwarzschild primary. The secondary is located in front of the primary focus and provides a magnification of 4, while the system has a plate scale of 28 microns arc/sec and a length of 1.9 m. The design, tolerance specification, fabrication and performance at visible and X-ray wavelengths of this optical system are described

Collective processes of an ensemble of spin-1/2 particles

When the dynamics of a spin ensemble are expressible solely in terms of symmetric processes and collective spin operators, the symmetric collective states of the ensemble are preserved. These many-body states, which are invariant under particle relabeling, can be efficiently simulated since they span a subspace whose dimension is linear in the number of spins. However, many open system dynamics break this symmetry, most notably when ensemble members undergo identical, but local, decoherence. In this paper, we extend the definition of symmetric collective states of an ensemble of spin-1/2 particles in order to efficiently describe these more general collective processes. The corresponding collective states span a subspace which grows quadratically with the number of spins. We also derive explicit formulae for expressing arbitrary identical, local decoherence in terms of these states.Comment: 12 pages, see 0805.2910 for simulations using these method

Efficient feedback controllers for continuous-time quantum error correction

We present an efficient approach to continuous-time quantum error correction that extends the low-dimensional quantum filtering methodology developed by van Handel and Mabuchi [quant-ph/0511221 (2005)] to include error recovery operations in the form of real-time quantum feedback. We expect this paradigm to be useful for systems in which error recovery operations cannot be applied instantaneously. While we could not find an exact low-dimensional filter that combined both continuous syndrome measurement and a feedback Hamiltonian appropriate for error recovery, we developed an approximate reduced-dimensional model to do so. Simulations of the five-qubit code subjected to the symmetric depolarizing channel suggests that error correction based on our approximate filter performs essentially identically to correction based on an exact quantum dynamical model

Supporting reinterpretation in computer-aided conceptual design

This paper presents research that aims to inform the development of computational tools that better support design exploration and idea transformation - key objectives in conceptual design. Analyses of experimental data from two fields - product design and architecture - suggest that the interactions of designers with their sketches can be formalised according to a finite number of generalised shape rules defined within a shape grammar. Such rules can provide a basis for the generation of alternative design concepts and they have informed the development of a prototype shape synthesis system that supports dynamic reinterpretation of shapes in design activity. The notion of 'sub-shapes' is introduced and the significance of these to perception, recognition and the development of emergent structures is discussed. The paper concludes with some speculation on how such a system might find application in a range of design fields

The young stellar population of Lynds 1340. An infrared view

We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low and intermediate-mass stars. Our goals are to identify and characterise the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects from the Spitzer and WISE data bases using various published color criteria, and classified them based on the slope of the spectral energy distribution. We identified 170 Class II, 27 Flat SED, and Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of young stellar objects shows three groups, associated with the three major molecular clumps of L1340, each consisting of less than 100 members, including both pre-main sequence stars and embedded protostars. New Herbig--Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.Comment: 73 pages, 33 figures, 15 tables. Accepted for publication in ApJ

Spontaneous Iliopsoas Hematoma following Microvascular Free Tissue Transfer.

Spontaneous hematoma within the iliopsoas muscle (SIH) is a rare complication most commonly seen in coagulopathic patients. Often, patients undergoing microvascular free tissue transfer are anticoagulated for anastomotic patency. Here we describe two cases of postoperative SIH following contralateral anterolateral thigh (ALT) free tissue transfer for reconstruction of oncologic head and neck defects. Both patients described hip pain after mobilization and had a corresponding acute blood loss anemia. Diagnosis of SIH was confirmed by CT and both patients were managed conservatively. Given that anticoagulation is a common practice following head and neck free tissue transfer, surgeons should be aware of this potential complication

Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br and CF3I

Using synchrotron radiation negative ions have been detected by mass spectrometry following vacuum-UV photoexcitation of trifluorochloromethane (CF$_3$Cl), trifluorobromomethane (CF$_3$Br) and trifluoroiodomethane (CF$_3$I). The anions F$^-$, X$^-$, F$_2^-$, FX$^-$, CF$^-$, CF$_2^-$ and CF$_3^-$ were observed from all three molecules, where X = Cl, Br or I, and their ion yields recorded in the range 8-35 eV. With the exception of Br$^-$ and I$^-$, the anions observed show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Dissociative electron attachment, following photoionization of CF$_3$Br and CF$_3$I as the source of low-energy electrons, is shown to dominate the observed Br$^-$ and I$^-$ signals, respectively. Cross sections for ion-pair formation are put on to an absolute scale by calibrating the signal strengths with those of F$^-$ from both SF$_6$ and CF$_4$. These anion cross sections are normalized to vacuum-UV absorption cross sections, where available, and the resulting quantum yields are reported. Anion appearance energies are used to calculate upper limits to 298 K bond dissociation energies for $D^0$(CF$_3$-X) which are consistent with literature values. We report new data for $D^0$(CF$_2$I$^-$-F) ≤ 2.7 ± 0.2 eV and $\Delta_fH^0_{298}$ (CF$_2$I$^+$) ≤ (598 ± 22) kJ mol$^{-1}$. No ion-pair formation is observed below the ionization energy of the parent molecule for CF$_3$Cl and CF$_3$Br, and only weak signals (in both I$^-$ and F$^-$) are detected for CF$_3$I. These observations suggest neutral photodissociation is the dominant exit channel to Rydberg state photoexcitation at these lower energies

A study of the phase transition in the usual statistical model for nuclear multifragmentation

We use a simplified model which is based on the same physics as inherent in most statistical models for nuclear multifragmentation. The simplified model allows exact calculations for thermodynamic properties of systems of large number of particles. This enables us to study a phase transition in the model. A first order phase transition can be tracked down. There are significant differences between this phase transition and some other well-known cases