Surface textures and other features of diamonds

The results of the study of more than 11 000 diamonds, from thirty kimberlite and placer deposit localities, are reported. Forty-one pristine surface textures are distinguished, including twelve which are described for the first time. Only two surface textures are ascribed to crystal growth. The others are considered to result from crystal resorption and etching although internal features, such as growth stratification and dislocation planes, are expressed in some cases. The results of etching experiments on diamond are reviewed. Oxidation is considered to be responsible for most of the resorption and etching of diamonds in nature and neither pure graphitization nor dissolution appears to be important

Optical studies on diamond surfaces

A brief review of the existing information on diamonds, including their physical properties and characteristic growth and solution features, is given in Part I. Part II deals with a short account of all the experimental techniques used in the present optical and interferometric studies of the microstructures of diamonds. Although Octahedron diamonds occur more frequently than the dodecahedron, yet in some mines the dodecahedron diamonds dominate not only in quantity but also in size. This fact is not consistent with the commonly accepted view that the dodecahedron form has developed due to the solution of Octahedron faces. It is expected that the present investigations on the microstructures of diamonds will throw some light on the conditions of their growth. The microstructures of dodecahedron diamonds are classified under two headings, namely (i) rare type of microstructures and (ii) common type of microstructures. Part III deals with the rare type of microstructures and in Chapter 3 are described unusual circular patterns which have been observed on three dodecahedral diamonds. Certain circular features which were illustrated by Sutton in 1928 with pencilled drawings resemble those described here. These features consist of slightly raised circular discs usually placed eccentrically one over the other and at times are overlapping and intersecting each other. The origin of these features has been discussed and their formation is attributed to a mechanism in which it is shown that liquid or gaseous bubbles were sticking on the faces of the crystal whilst the dissolution of the dodecahedral faces was taking place everywhere excepting the regions which were protected by the bubbles. Chapter IV deals with a brief review of the etch methods and the information on artificial etching of diamonds. Natural etch patterns not observed previously on the dodecahedron diamonds are also described in this Chapter. According to the experimental evidence these etch pits are expected to be canoe-shaped and perpendicular to the longer diagonal of the rhombic face. However, the natural etch pits are (a) canoe-shaped (b) oblong-shaped and (c) oval-shaped. The deviation in shape of these etch pits and their occurrence is explained. These natural etch pits uniquely arrange themselves in circular arrays and this has been attributed to the formation of liquid bubbles on the surface before natural etching started. Common microstructures of dodecahedral faces of diamonds as observed are (i) striations (ii) irregular network and (iii) rectilinear parallelogram network. It is suggested that the striations and irregular network owe their existence to growth and that subsequent solution of the faces reveals these features. The rectilinear parallelogram network is considered to be due to the solution of the faces of diamond which shows up those (111) planes along which diamond grows. These (111) planes are those which intersect (110) faces normally. The study of common microstructures of dodecahedron diamonds affords a further confirmation of the view that the dodecahedral faces of diamond are much more susceptible to solution than the octahedron faces. In Appendix A, observations made on trigons occurring on the octahedron faces of diamonds are described. The presence of a flat-bottomed trigon whose base is at the same level as a neighbouring area, the occurrence of slip and the presence of growth hills only on octahedron diamonds appears to be conclusive proof that they are growth features. In Appendix B, some graphitization experiments are given and it is concluded that graphitization sets in at a slow a temperature as 1060&deg;C. when diamond is heated in a graphite crucible in an atmosphere of Nitrogen.<p

Joint Laver diamonds and grounded forcing axioms

I explore two separate topics: the concept of jointness for set-theoretic guessing principles, and the notion of grounded forcing axioms. A family of guessing sequences is said to be joint if all of its members can guess any given family of targets independently and simultaneously. I primarily investigate jointness in the case of various kinds of Laver diamonds. In the case of measurable cardinals I show that, while the assertions that there are joint families of Laver diamonds of a given length get strictly stronger with increasing length, they are all equiconsistent. This is contrasted with the case of partially strong cardinals, where we can derive additional consistency strength, and ordinary diamond sequences, where large joint families exist whenever even one diamond sequence does. Grounded forcing axioms modify the usual forcing axioms by restricting the posets considered to a suitable ground model. I focus on the grounded Martin's axiom which states that Martin's axioms holds for posets coming from some ccc ground model. I examine the new axiom's effects on the cardinal characteristics of the continuum and show that it is quite a bit more robust under mild forcing than Martin's axiom itself.Comment: This is my PhD dissertatio

Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund's rule, underscreened Kondo effect and quantum phase transitions

We review here some universal aspects of the physics of two-electron molecular transistors in the absence of strong spin-orbit effects. Several recent quantum dots experiments have shown that an electrostatic backgate could be used to control the energy dispersion of magnetic levels. We discuss how the generically asymmetric coupling of the metallic contacts to two different molecular orbitals can indeed lead to a gate-tunable Hund's rule in the presence of singlet and triplet states in the quantum dot. For gate voltages such that the singlet constitutes the (non-magnetic) ground state, one generally observes a suppression of low voltage transport, which can yet be restored in the form of enhanced cotunneling features at finite bias. More interestingly, when the gate voltage is controlled to obtain the triplet configuration, spin S=1 Kondo anomalies appear at zero-bias, with non-Fermi liquid features related to the underscreening of a spin larger than 1/2. Finally, the small bare singlet-triplet splitting in our device allows to fine-tune with the gate between these two magnetic configurations, leading to an unscreening quantum phase transition. This transition occurs between the non-magnetic singlet phase, where a two-stage Kondo effect occurs, and the triplet phase, where the partially compensated (underscreened) moment is akin to a magnetically "ordered" state. These observations are put theoretically into a consistent global picture by using new Numerical Renormalization Group simulations, taylored to capture sharp finie-voltage cotunneling features within the Coulomb diamonds, together with complementary out-of-equilibrium diagrammatic calculations on the two-orbital Anderson model. This work should shed further light on the complicated puzzle still raised by multi-orbital extensions of the classic Kondo problem.Comment: Review article. 16 pages, 17 figures. Minor corrections and extra references added in V

CaSiO3-walstromite inclusions in super-deep diamonds

Diamonds are considered the unique way to trap and convey real fragments of deep material to the surface of our planet. Over the last thirty years, great strides have been made in understanding of Earth\u2019s lower mantle, mainly thanks to technological and instrumental advances; nevertheless, it is only in the last two decades that a whole range of inclusion parageneses derived from the lower mantle was discovered in diamonds from S\ue3o Luiz (Brazil) (Kaminsky, 2008 and references therein), thereby establishing a \u201cwindow\u201d into the lower mantle. These so-called super-deep diamonds form at depths greater than lithospheric diamonds, more precisely between 300 and 800 km depth, and contain mostly ferropericlase, enstatite (believed to be derived from MgSi-perovskite) and CaSiO3- walstromite (believed to be derived from CaSiO3-perovskite). Even though CaSiO3 not only adopts the perovskite structure with increased pressure and temperature, but also it is considered the dominant Ca-bearing phase in the Earth\u2019s lower mantle (Tamai and Yagi, 1989), at the present day there are no reliable literature data on the pressure at which CaSiO3 crystallizes within diamonds. In order to obtain for the first time a pressure of formation value for CaSiO3-walstromite, several inclusions still trapped in a diamond coming from Juina (Mato Grosso, Brazil) were investigated both by in-situ microRaman spectroscopy and in-situ single-crystal X-ray diffraction. First, we applied \u201csingle-inclusion elastic barometry\u201d as improved by Angel et al. (2014) to determine the pressure of formation of the diamond-inclusion pairs. Starting from the maximum remnant pressure value ever reported (Joswig et al., 2003) and adopting the thermoelastic parameters already present in literature (Swamy and Dubrovinsky, 1997; Liu et al., 2012), we obtained an appar- ent entrapment pressure of 3c7.1 GPa, corresponding to 3c250 km, at 1500 K. The presence of fractures around the inclusions indicates this is a minimum estimate, and it is possible that the entrapment pressure falls at least into the stability field of Ca2SiO4-larnite + CaSi2O5-titanite. In support of this hypothesis we secondly compared our Raman spectra with reference spectra of the same phases obtained from an experimental product of Gasparik et al. (1994). Our preliminary results indicate in at least one inclusion the coexistence of CaSiO3-walstromite + Ca2SiO4-larnite, suggesting that CaSiO3-walstromite forms in sub-lithospheric conditions from the back transfor- mation from CaSiO3-perovskite. Further investigations are in progress in order to find evidence of CaSi2O5-titanite in these inclusions

DIAMONDS: a new Bayesian Nested Sampling tool. Application to Peak Bagging of solar-like oscillations

To exploit the full potential of Kepler light curves, sophisticated and robust analysis tools are now required more than ever. Characterizing single stars with an unprecedented level of accuracy and subsequently analyzing stellar populations in detail are fundamental to further constrain stellar structure and evolutionary models. We developed a new code, termed Diamonds, for Bayesian parameter estimation and model comparison by means of the nested sampling Monte Carlo (NSMC) algorithm, an efficient and powerful method very suitable for high-dimensional and multi-modal problems. A detailed description of the features implemented in the code is given with a focus on the novelties and differences with respect to other existing methods based on NSMC. Diamonds is then tested on the bright F8 V star KIC~9139163, a challenging target for peak-bagging analysis due to its large number of oscillation peaks observed, which are coupled to the blending that occurs between $\ell=2,0$ peaks, and the strong stellar background signal. We further strain the performance of the approach by adopting a 1147.5 days-long Kepler light curve. The Diamonds code is able to provide robust results for the peak-bagging analysis of KIC~9139163. We test the detection of different astrophysical backgrounds in the star and provide a criterion based on the Bayesian evidence for assessing the peak significance of the detected oscillations in detail. We present results for 59 individual oscillation frequencies, amplitudes and linewidths and provide a detailed comparison to the existing values in the literature. Lastly, we successfully demonstrate an innovative approach to peak bagging that exploits the capability of Diamonds to sample multi-modal distributions, which is of great potential for possible future automatization of the analysis technique.Comment: 22 pages, 14 figures, 3 tables. Accepted for publication in A&

Multilevel MDA-Lite Paris Traceroute

Since its introduction in 2006-2007, Paris Traceroute and its Multipath Detection Algorithm (MDA) have been used to conduct well over a billion IP level multipath route traces from platforms such as M-Lab. Unfortunately, the MDA requires a large number of packets in order to trace an entire topology of load balanced paths between a source and a destination, which makes it undesirable for platforms that otherwise deploy Paris Traceroute, such as RIPE Atlas. In this paper we present a major update to the Paris Traceroute tool. Our contributions are: (1) MDA-Lite, an alternative to the MDA that significantly cuts overhead while maintaining a low failure probability; (2) Fakeroute, a simulator that enables validation of a multipath route tracing tool's adherence to its claimed failure probability bounds; (3) multilevel multipath route tracing, with, for the first time, a Traceroute tool that provides a router-level view of multipath routes; and (4) surveys at both the IP and router levels of multipath routing in the Internet, showing, among other things, that load balancing topologies have increased in size well beyond what has been previously reported as recently as 2016. The data and the software underlying these results are publicly available.Comment: Preprint. To appear in Proc. ACM Internet Measurement Conference 201

0-π\pi quantum transition in a carbon nanotube Josephson junction: universal phase dependence and orbital degeneracy

We investigate experimentally the supercurrent in a clean carbon nanotube quantum dot, close to orbital degeneracy, connected to superconducting leads in a regime of strong competition between local electronic correlations and superconducting proximity effect. For an odd occupancy of the dot and intermediate coupling to the reservoir, the Kondo effect can develop in the normal state and screen the local magnetic moment of the dot. This leads to singlet-doublet transitions that strongly affect the Josephson effect in a single-level quantum dot: the sign of the supercurrent changes from positive to negative (0 to $\pi$-junction). In the regime of strongest competition between the Kondo effect and proximity effect, meaning that the Kondo temperature equals the superconducting gap, the magnetic state of the dot undergoes a first order quantum transition induced by the superconducting phase difference across the junction. This is revealed experimentally by anharmonic current-phase relations. In addition, the very specific electronic configuration of clean carbon nanotubes, with two nearly orbitally degenerated states, leads to different physics depending whether only one or both quasi-degenerate upper levels of the dots participate to transport, which is determined by their occupancy and relative widths. When the transport of Cooper pairs takes place through only one of these levels, we find that the phase diagram of the phase-dependent 0-$\pi$ transition is a universal characteristic of a discontinuous level-crossing quantum transition at zero temperature. In the case were two levels participate to transport, the nanotube Josephson current exhibits a continuous 0-$\pi$ transition, independent of the superconducting phase, revealing a different physical mechanism of the transition.Comment: 14 pages, 12 figure

How Community Institutions Create Economic Advantage: Jewish Diamond Merchants in New York

This paper argues that Jewish merchants have historically dominated the diamond industry because of their ability to reliably implement diamond credit sales. Success in the industry requires enforcing executory agreements that are beyond the reach of public courts, and Jewish diamond merchants enforce such contracts with a reputation mechanism supported by a distinctive set of industry, family, and community institutions. An industry arbitration system publicizes promises that are not kept. Intergenerational legacies induce merchants to deal honestly through their very last transaction, so that their children may inherit valuable livelihoods. And ultra-Orthodox Jews, for whom participation in their communities is paramount, provide important value-added services to the industry without posing the threat of theft and flight