Tiny Shifts Research Articles

Flexible 2D Crystals of Polycyclic Aromatics Stabilized by Static Distortion Waves.

The epitaxy of many organic films on inorganic substrates can be classified within the framework of rigid lattices which helps to understand the origin of energy gain driving the epitaxy of the films. Yet, there are adsorbate–substrate combinations with distinct mutual orientations for which this classification fails and epitaxy cannot be explained within a rigid lattice concept. It has been proposed that tiny shifts in atomic positions away from ideal lattice points, so-called static distortion waves (SDWs), are responsible for the observed orientational epitaxy in such cases. Using low-energy electron diffraction and scanning tunneling microscopy, we provide direct experimental evidence for SDWs in organic adsorbate films, namely hexa-peri-hexabenzocoronene on graphite. They manifest as wave-like sub-Ångström molecular displacements away from an ideal adsorbate lattice which is incommensurate with graphite. By means of a density-functional-theory based model, we show that, due to the flexibility in the adsorbate layer, molecule–substrate energy is gained by straining the intermolecular bonds and that the resulting total energy is minimal for the observed domain orientation, constituting the orientational epitaxy. While structural relaxation at an interface is a common assumption, the combination of the precise determination of the incommensurate epitaxial relation, the direct observation of SDWs in real space, and their identification as the sole source of epitaxial energy gain constitutes a comprehensive proof of this effect.

Negotiating Uncertainty

In this article, we deploy the concept of 'affect' to explore processes of state formation in contemporary Peru. Drawing on ethnography concerning a controversial engineering project in the Sacred Valley, we show how the state emerges as an affective force in the ambivalent spaces opened up by the slippages between the stable certainties promised by regulatory frameworks and the doubts generated by the ambiguities they pose. Tracing the tensions, gestures, and tiny shifts in perspective that punctuate an encounter between engineers and local politicians, we complicate the notion that a pre-existing state induces affects in political subjects. Instead, we show how the state emerges as a virtual force—neither quite present nor absent—in an uncertain, highly political field of negotiation.

Tracing part-per-billion line shifts with direct-frequency-comb Vernier spectroscopy

Accurate frequency measurements of molecular transitions around $2 \ensuremath{\mu}\mathrm{m}$ are performed by using a direct-frequency-comb spectroscopy approach that combines an ${\mathrm{Er}}^{+}$ frequency-comb oscillator at $1.5 \ensuremath{\mu}\mathrm{m}$, a Tm-Ho fiber amplifier, and a Fabry-Perot-filter, high-resolution dispersive spectrometer optical multiplex-detection system. This apparatus has unique performances in terms of a wide dynamic range to integrate the intensity per comb mode, which allows one to measure molecular absorption profiles with high precision. Spectroscopic information about transition frequencies and linewidths is very accurately determined. Relative frequency uncertainties of the order of a few parts in ${10}^{\ensuremath{-}9}$ are achieved for rovibrational transitions of the ${\mathrm{CO}}_{2}$ molecule around $5100 {\mathrm{cm}}^{\ensuremath{-}1}$. Moreover, tiny frequency shifts due to molecular collisions and interacting laser power using direct comb spectroscopy are investigated in a systematic way.

Simultaneous weak value amplification of angular Goos-Hänchen and Imbert-Fedorov shifts in partial reflection.

The optical analogue of quantum weak measurements has shown considerable promise for the amplification and observation of tiny optical beam shifts, namely Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts. Here, we demonstrate simultaneous weak value amplification of both the angular GH and the IF shifts in partial reflection of a fundamental Gaussian beam at planar dielectric interfaces. We employ pre and postselection schemes with appropriate linear polarization basis states for simultaneous weak measurements and amplification of both of these shifts. The experimentally observed enhancement of the beam shifts and their dependence on the angle of incidence are analyzed/interpreted via theoretical treatment of weak measurements.

Photonic spin Hall effect for precision metrology

The photonic spin Hall effect (SHE) is generally believed to be a result of an effective spin-orbit coupling, which describes the mutual influence of the spin (polarization) and the trajectory of the light beam. The photonic SHE holds great potential for precision metrology owing to the fact that the spin-dependent splitting in photonic SHE are sensitive to the physical parameter variations of different systems. Remarkably, using the weak measurements, this tiny spin-dependent shifts can be detected with the desirable accuracy so that the corresponding physical parameters can be determined. Here, we will review some of our works on using photonic SHE for precision metrology, such as measuring the thickness of nanometal film, identifying the graphene layers, detecting the strength of axion coupling in topological insulators, and determining the magneto-optical constant of magnetic film.

Diffraction studies under in situ electric field using a large-area hybrid pixel XPAD detector

A new experimental approach to perform in situ electric field diffraction on single crystals using an on-then-off pump–probe mode in situ (i.e. the field-switching method) with a synchrotron or a laboratory X-ray source is presented. Taking advantage of the fast readout of the XPAD hybrid pixel two-dimensional detector and its programmable functionalities, the operation mode of the detector has been customized to significantly increase the efficiency of the method. The very weak electric field-induced structural response of a piezoelectric crystal can be accurately measured. This allows the piezoelectric tensor to be precisely obtained from Δθ shifts while the structural variations can be modelled using a full set of ΔI/I data. The experimental method and methodology are detailed and tested as a case study on pure piezoelectric compounds belonging to the α-quartz family (SiO2 and GaAsO4 single crystals). Using the two scan modes developed, it is demonstrated that tiny Bragg angle shifts can be measured as well as small field-induced Bragg intensity variations (<1%). The relevance of measurements performed with an X-ray laboratory source is demonstrated: partial data sets collected at synchrotrons can be completed, but more interestingly, a large part of the study can now be realized in the laboratory (medium to strong intensity reflections) in a comparable data collection time.

ARE PULSING SOLITARY WAVES RUNNING INSIDE THE SUN?

A precise sequence of frequencies—detected four independent ways—is interpreted as a system of solitary waves below the Sun's convective envelope. Six future observational or theoretical tests of this idea are suggested. Wave properties (rotation rates, radial energy distribution, nuclear excitation strength) follow from conventional dynamics of global oscillation modes after assuming a localized nuclear term strong enough to perturb and hold mode longitudes into alignments that form families. To facilitate future tests, more details are derived for a system of two dozen solitary waves 2 ≤ l ≤ 25. Wave excitation by 3He and 14C burning is complex. It spikes by factors M 1 ≤ 103 when many waves overlap in longitude but its long-time average is M 2 ≤ 10. Including mixing can raise overall excitation to ~50 times that in a standard solar model. These spikes cause tiny phase shifts that tend to pull wave rotation rates toward their ideal values ∝[l(l + 1)]–1. A system like this would generate some extra nuclear energy in two spots at low latitude on opposite sides of the Sun. Each covers about 20° of longitude. Above a certain wave amplitude, the system starts giving distinctly more nuclear excitation to some waves (e.g., l = 9, 14, and 20) than to neighboring l values. The prominence of l = 20 has already been reported. This transition begins at temperature amplitudes ΔT/T = 0.03 in the solar core for a typical family of modes, which corresponds to δT/T ~ 0.001 for one of its many component oscillation modes.

High-Q optical sensors for chemical and biological analysis.

High-Q optical sensors for chemical and biological analysis.

The eye on the needle

Tiny gaze shifts, or microsaccades, have little function in the eye movement control system and were once thought to be suppressed during fine spatial judgements. A new study suggests that they are important for finely guided visuomotor tasks and may actively contribute to the acquisition of spatial information in the same way as do larger saccades.

Heinrich Heine and the Lied. By Susan Youens.

Writing about the German Lied can often seem a highly specialized affair, requiring the gift of aligning poetry and music to illuminate the detailed workings of a song. It demands a painstaking sifting of information to bring it to bear upon often tiny shifts of nuance, in which a world of meaning can reside for the sympathetic respondent. Writer and reader must conspire to treasure the uncovering of correspondences, and foster the belief that the experience of the lyric will be enhanced or renewed by finding new points of connection. Susan Youens is surely one of the most virtuosic of the Lieder specialists; her writing has transformed the listening habits of a generation of song enthusiasts through its ability to plot the ‘lightning bolts of realization’ within a song (p. 17). In this book the author's technique of distilling analytical insights, surveying the patterns of a composer's poetic response till she can home in on its key, is confirmed as second to none. The technique is often dazzling, but more crucial still perhaps is the aesthetic belief that underlies it. Youens makes it quite clear that, for her, much of the value of song lies in its hidden stories, the networks of associations that require an effort of the imagination to be drawn to the surface. ‘Effort’ is the key word here—at many points Youens describes her present book as an ‘endeavour’ that she has embarked upon. And one might characterize her exploration of composers’ responses to Heine's poetry as a battle royal with those who would underestimate the power of song to generate layers of meaning as worthy of this most complex of poets.

Pattern formation and directional and spatial ordering of edge dislocations in bulk GaN: Microphotoluminescence spectra and continuum elastic calculations

We present a detailed microphotoluminescence study of the long-range strain fields surrounding threading dislocations as well as their interaction and pattern formation in GaN bulk crystals. The stress patterns are detected by tiny energy shifts of the near-band-edge spectral lines and show a dipolelike stress state around the dislocation core of edge- or mixed-type dislocations, with an angular orientation coinciding with high-symmetry crystal directions. We detect tens of micrometers long linear lineups of edge dislocations with sizable effects on the local strain states and photoluminescence peak positions. With continuum elastic strain simulations, we demonstrate that the observed patterns of threading dislocations are energetically favorable. We calculated a binding energy per threading dislocation length of $50\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\ensuremath{\mu}\mathrm{m}$ against gliding of an edge dislocation within a lineup of edge dislocations of parallel Burgers vector orientation.

WE‐D‐L100J‐07: High‐Resolution Digital Ultrasonic Thermometers

Purpose: To develop and test 1) fully digital μK‐resolution ultrasonic thermometer for non‐invasive measurements of absorbed radiation dose in water; 2) rapid ultrasonic 2D temperature mapping system for precise characterization of radiation beam intensity profiles. Method and Materials: Monitoring tiny phase shifts of ultrasonic signals in water heated by ionizing radiation allows assessing water temperature changes at the μK level. Instead of the analog frequency‐driven Pulsed Phase‐Locked Loop (PPLL) used in the earlier work to track signal phase, the current system relies on fast digital phase algorithms that extract signal delay with resolution of 100ppb and better. Another ultrasonic system was built to produce 2D temperature maps in water. This system contains a 128‐element, 14″‐diameter circular transducer array operating in a tomographic fan‐beam data acquisition mode. The system acquires temperature maps in seconds and allows monitoring evolution of thermal processes in time. Results: The single‐channel digital ultrasonic thermometer demonstrated resolution equivalent or better than analog PPLL‐based prototype at overall lower noise level. The 2D temperature mapping system was constructed and went though a preliminary testing round. It monitored evolution of temperature profile in the cylindrical tank every 3–4 seconds acquiring each time a 64‐projection data set with 45 rays per projection. After extracting phase information from the acoustic waveforms the system reconstructed a sequence of phase shift images and converted them to temperature maps using newly developed calibration procedure. The maps were combined into movies to watch temperature evolution dynamics. Conclusion: The digital high‐resolution ultrasonic thermometer demonstrated performance improvement and will replace its analog predecessor in the radiation‐testing lab. The 2D ultrasonic temperature mapping system was successfully tested with a light radiation heating source. We plan to continue characterizing its spatial and temperature resolution and incorporate all findings into a next‐generation prototype for ionizing radiation testing.Research sponsored by NIST.

Analysis of the peculiar shift of the low-frequency end of a variable photonic band gap

The effect of the variation of a rod’s dielectric constant on the photonic band gap in a two-dimensional square lattice structure photonic crystal is studied in this paper. The effects were calculated by FDTD algorithm and some peculiar variation properties were obtained. By consecutively changing the dielectric constant of the rod over certain wide ranges and fixing that of the background, the low-frequency end of the TM band gap in low frequency regions reveals very tiny shifts which to some extent can be treated as fixed. This is primarily due to the fact that the high-e region in the crystal is nearly unchanged, hence, the concentrated energy of the low frequency mode changes only slightly. This effect does not exist for materials whose dielectrics are varied over wide ranges. We propose an alternative method using 2D core-shell photonic crystals. The final results of the band calculation show that the gap maps of the core-shell cases closely match those of the ideal case. Such peculiar changes in the photonic band gap have wide application prospects.

Pressure dependence of the magnetic structures and excitations in the giant magnetostriction compound TbCu 2

A small shift of magnetic excitation energies is expected when applying pressure on a compound with large magnetostriction. We were able to observe these tiny shifts by inelastic neutron scattering on the giant magnetostriction (GMS) compound TbCu 2. The experiments were performed at 4 and 60 K using a McWhan pressure cell. The peaks in the spectra were shifted by 0.4 meV to higher energies at the maximum pressure of 2 GPa by the magnetoelastic interaction. This strong interaction of the crystal electric field (CF) with the lattice may be liable for the GMS effect. Moreover, neutron diffraction experiments show a weak but noticeable influence of strong external pressure on the magnetic structure of TbCu 2. The ambient pressure magnetic propagation vector τ=( 2 3 1 0) at low temperatures is also preserved under pressure. The data indicate a non-collinear magnetic structure. In addition to the CF the exchange interaction also changes under pressure and leads to a slightly modified magnetic propagation vector in the vicinity of T N.

Are mirror worlds opaque?

Over the last few years, many close orbiting (∼0.05 A.U.) large mass planets (∼ M J ) of nearby stars have been discovered. Their existence has been inferred from tiny Doppler shifts in the light from the star and in one case a transit has been observed. Because ordinary planets are not expected to be able to form this close to ordinary stars due to the high temperatures, it has been speculated that the close-in large planets are in fact exotic heavenly bodies made of mirror matter. We show that the accretion of ordinary matter onto the mirror planet (from, e.g., the solar wind from the host star) should make the mirror planet opaque to ordinary radiation with an effective radius ( R p ) large enough to explain the measured size of the transiting close-in extrasolar planet, HD209458b. Furthermore, we obtain the rough prediction that R p∝ T s/M p (where T s , is the surface temperature of the ordinary matter in the mirror planet and M p is the mass of the mirror planet) which will be tested in the near future as more transiting planets are found. We also show that the mirror world interpretation of the close-in extra solar planets explains the low albedo of τ Boo b because the large estimated mass of τ Boo b (∼7 M J ) implies a small effective radius of R p ≈0.5 R J for τ Boo.

Have mirror planets been observed?

Over the last few years, several close orbiting (∼0.05 AU) large mass planets ( M∼ M Jupiter) of nearby stars have been discovered. Their existence has been inferred from tiny doppler shifts in the light from the star. We suggest that these planets may be made of mirror matter. We also suggest that some stars such as our sun may also have a similar amount of mirror matter, which has escaped detection.

Observation of Energy-Shifted Gamma-Ray Absorption by133Cs Nucleus Placed in Finite Space

We report the first reliable observation of the tiny shifts of energy levels of a nucleus placed between two parallel metallic plates. We observed the absorption of the 81 keV gamma ray from 133 Cs induced by the β-decay of 133 Ba in a * BaTiO 3 compound. This Mossbauer experiment was carried out at 4.2 K with the absorber placed between two silicon plates with gold coating. The observed shifts are around 0.95 neV (equivalent to 0.007 mm/s) for the distance of about 2 mm between the two plates.

Les avatars de Varāha en Himalaya

Marie Lecomte-Tilouine, "The Metamorphoses of Varāha in the Himalayas". This article reports the results of an inquiry into the god Baraha in a region of Central Nepal. It examines the various motifs attached to each of its forms and puts forward those which are shared by these manifestations and their classical homonym, the avatar of Vishnu as a boar. Thanks to the relatively large range of her regional research, the author have been able to show a chain of successive tiny shifts of symbolical attributes of these forms from North to South; on the other hand, from West to East, the Kali Gandaki river forms a kind of cultural boundary, with very different characteristics on each of its banks.