Concept: Fundamental physics concepts
Spatial resolution, spectral contrast and occlusion are three major bottlenecks for non-invasive inspection of complex samples with current imaging technologies. We exploit the sub-picosecond time resolution along with spectral resolution provided by terahertz time-domain spectroscopy to computationally extract occluding content from layers whose thicknesses are wavelength comparable. The method uses the statistics of the reflected terahertz electric field at subwavelength gaps to lock into each layer position and then uses a time-gated spectral kurtosis to tune to highest spectral contrast of the content on that specific layer. To demonstrate, occluding textual content was successfully extracted from a packed stack of paper pages down to nine pages without human supervision. The method provides over an order of magnitude enhancement in the signal contrast and can impact inspection of structural defects in wooden objects, plastic components, composites, drugs and especially cultural artefacts with subwavelength or wavelength comparable layers.
Wettability is the affinity of a liquid for a solid surface. For energetic reasons, macroscopic drops of liquid form nearly spherical caps. The degree of wettability is then captured by the contact angle where the liquid-vapor interface meets the solid-liquid interface. As droplet volumes shrink to the scale of attoliters, however, surface interactions become significant, and droplets assume distorted shapes. In this regime, the contact angle becomes ambiguous, and a scalable metric for quantifying wettability is needed, especially given the emergence of technologies exploiting liquid-solid interactions at the nanoscale. Here we combine nanoscale experiments with molecular-level simulation to study the breakdown of spherical droplet shapes at small length scales. We demonstrate how measured droplet topographies increasingly reveal non-spherical features as volumes shrink. Ultimately, the nanoscale droplets flatten out to form layer-like molecular assemblies at the solid surface. For the lack of an identifiable contact angle at small scales, we introduce a droplet’s adsorption energy density as a new metric for a liquid’s affinity for a surface. We discover that extrapolating the macroscopic idealization of a drop to the nanoscale, though it does not geometrically resemble a realistic droplet, can nonetheless recover its adsorption energy if line tension is included.
The negatively charged nitrogen vacancy (NV(-)) center in diamond is the focus of widespread attention for applications ranging from quantum information processing to nanoscale metrology. Although most work so far has focused on the NV(-) optical and spin properties, control of the charge state promises complementary opportunities. One intriguing possibility is the long-term storage of information, a notion we hereby introduce using NV-rich, type 1b diamond. As a proof of principle, we use multicolor optical microscopy to read, write, and reset arbitrary data sets with two-dimensional (2D) binary bit density comparable to present digital-video-disk (DVD) technology. Leveraging on the singular dynamics of NV(-) ionization, we encode information on different planes of the diamond crystal with no cross-talk, hence extending the storage capacity to three dimensions. Furthermore, we correlate the center’s charge state and the nuclear spin polarization of the nitrogen host and show that the latter is robust to a cycle of NV(-) ionization and recharge. In combination with super-resolution microscopy techniques, these observations provide a route toward subdiffraction NV charge control, a regime where the storage capacity could exceed present technologies.
It is believed that not all quantum systems can be simulated efficiently using classical computational resources. This notion is supported by the fact that it is not known how to express the partition function in a sign-free manner in quantum Monte Carlo (QMC) simulations for a large number of important problems. The answer to the question-whether there is a fundamental obstruction to such a sign-free representation in generic quantum systems-remains unclear. Focusing on systems with bosonic degrees of freedom, we show that quantized gravitational responses appear as obstructions to local sign-free QMC. In condensed matter physics settings, these responses, such as thermal Hall conductance, are associated with fractional quantum Hall effects. We show that similar arguments also hold in the case of spontaneously broken time-reversal (TR) symmetry such as in the chiral phase of a perturbed quantum Kagome antiferromagnet. The connection between quantized gravitational responses and the sign problem is also manifested in certain vertex models, where TR symmetry is preserved.
OBJECTIVE: To characterise the influence of diet on abdominal symptoms, anal gas evacuation, intestinal gas distribution and colonic microbiota in patients complaining of flatulence. DESIGN: Patients complaining of flatulence (n=30) and healthy subjects (n=20) were instructed to follow their usual diet for 3 days (basal phase) and to consume a high-flatulogenic diet for another 3 days (challenge phase). RESULTS: During basal phase, patients recorded more abdominal symptoms than healthy subjects in daily questionnaires (5.8±0.3 vs 0.4±0.2 mean discomfort/pain score, respectively; p=<0.0001) and more gas evacuations by an event marker (21.9±2.8 vs 7.4±1.0 daytime evacuations, respectively; p=0.0001), without differences in the volume of gas evacuated after a standard meal (262±22 and 265±25 mL, respectively). On flatulogenic diet, both groups recorded more abdominal symptoms (7.9±0.3 and 2.8±0.4 discomfort/pain, respectively), number of gas evacuations (44.4±5.3 and 21.7±2.9 daytime evacuations, respectively) and had more gas production (656±52 and 673±78 mL, respectively; p<0.05 vs basal diet for all). When challenged with flatulogenic diet, patients' microbiota developed instability in composition, exhibiting variations in the main phyla and reduction of microbial diversity, whereas healthy subjects' microbiota were stable. Taxa from Bacteroides fragilis or Bilophila wadsworthia correlated with number of gas evacuations or volume of gas evacuated, respectively. CONCLUSIONS: Patients complaining of flatulence have a poor tolerance of intestinal gas, which is associated with instability of the microbial ecosystem.
That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.
Spin-transfer torques offer great promise for the development of spin-based devices. The effects of spin-transfer torques are typically analysed in terms of adiabatic and non-adiabatic contributions. Currently, a comprehensive interpretation of the non-adiabatic term remains elusive, with suggestions that it may arise from universal effects related to dissipation processes in spin dynamics, while other studies indicate a strong influence from the symmetry of magnetization gradients. Here we show that enhanced magnetic imaging under dynamic excitation can be used to differentiate between non-adiabatic spin-torque and extraneous influences. We combine Lorentz microscopy with gigahertz excitations to map the orbit of a magnetic vortex core with <5 nm resolution. Imaging of the gyrotropic motion reveals subtle changes in the ellipticity, amplitude and tilt of the orbit as the vortex is driven through resonance, providing a robust method to determine the non-adiabatic spin torque parameter β=0.15±0.02 with unprecedented precision, independent of external effects.
Electronic carriers in graphene show a high carrier mobility at room temperature. Thus, this system is widely viewed as a potential future charge-based high-speed electronic material to complement-or replace-silicon. At the same time, the spin properties of graphene have suggested improved capability for spin-based electronics or spintronics and spin-based quantum computing. As a result, the detection, characterization and transport of spin have become topics of interest in graphene. Here we report a microwave photo-excited transport study of monolayer and trilayer graphene that reveals an unexpectedly strong microwave-induced electrical response and dual microwave-induced resonances in the dc resistance. The results suggest the resistive detection of spin resonance, and provide a measurement of the g-factor, the spin relaxation time and the sub-lattice degeneracy splitting at zero magnetic field.
- Journal of the Royal Society, Interface / the Royal Society
- Published almost 8 years ago
A new tool for visualization and analysis of system dynamics is introduced: the phasegram. Its application is illustrated with both classical nonlinear systems (logistic map and Lorenz system) and with biological voice signals. Phasegrams combine the advantages of sliding-window analysis (such as the spectrogram) with well-established visualization techniques from the domain of nonlinear dynamics. In a phasegram, time is mapped onto the x-axis, and various vibratory regimes, such as periodic oscillation, subharmonics or chaos, are identified within the generated graph by the number and stability of horizontal lines. A phasegram can be interpreted as a bifurcation diagram in time. In contrast to other analysis techniques, it can be automatically constructed from time-series data alone: no additional system parameter needs to be known. Phasegrams show great potential for signal classification and can act as the quantitative basis for further analysis of oscillating systems in many scientific fields, such as physics (particularly acoustics), biology or medicine.
A major obstacle to the efficient production of antibody conjugates for therapy and diagnosis is the non-ideal performance of commonly used chemical methods for the attachment of effector-molecules to the antibody of interest. Here we demonstrate that this limitation can be simply addressed using 3,4-substituted maleimides to bridge and thus functionalize disulfide bonds to generate homogeneous antibody conjugates. This one-step conjugation reaction is fast, site-specific, quantitative and generates products with full binding activity, good plasma stability and the desired functional properties. Furthermore, the rigid nature of this modification by disulfide bridging enables the successful detection of antigen with a spin labeled antibody fragment by continuous-wave electron paramagnetic resonance (cw-EPR), which we report here for the first time. Antigen detection is concentration dependent, observable in human blood and allows the discrimination of fragments with different binding affinity. We envisage broad potential for antibody based in-solution diagnostic methods by EPR or ‘spinostics’.