Large Frequency Shift Research Articles

Recognition of Melamine by Chromium Tricarbonyl (Thio)barbituric Acid Derivatives: Theoretical Insight into Multiple Hydrogen‐Bond Modes

AbstractMelamine‐contaminated milk products continually emerge in recent years and cause disease. Therefore, how to swiftly and efficiently differentiate melamine from protein becomes an urgent issue. In this work, three neutral receptors p‐dimethylaminobenzaldehyde‐barbituric acid chromium tricarbonyl (PBC), p‐dimethylaminobenzaldehyde‐2‐thiobarbituric acid chromium tricarbonyl (2‐PTC), and p‐dimethylaminobenzaldehyde‐4‐thiobarbituric acid chromium tricarbonyl (4‐PTC) were constructed for recognition of melamine, and their non‐covalent interactions were systematically studied using density functional theory and several theoretical analysis methods. Our results suggest that melamine can be theoretically recognized by receptors PBC and 2‐/4‐PTC due to the formation of multiple hydrogen bonds upon complexation, indicating the good detecting capability of the Cr(CO)3‐based (thio)barbituric acid moiety. Nevertheless, the IR analysis results show the receptors 2‐/4‐PTC cannot distinctly detect melamine by evident frequency shift of metal carbonyl. Therefore, we further proposed a structural modification strategy by introducing the cyano group into the (thio)barbituric acid moiety, and the corresponding IR analysis exhibits large frequency shift of metal carbonyl, indicating the potential of modified receptors in the infrared neutral molecular recognition of melamine. The results reported herein will be very useful in the design of potent receptors distinguishing melamine from protein.

Conformational Ensembles of Calmodulin Revealed by Nonperturbing Site-Specific Vibrational Probe Groups.

Seven native residues on the regulatory protein calmodulin, including three key methionine residues, were replaced (one by one) by the vibrational probe amino acid cyanylated cysteine, which has a unique CN stretching vibration that reports on its local environment. Almost no perturbation was caused by this probe at any of the seven sites, as reported by CD spectra of calcium-bound and apo calmodulin and binding thermodynamics for the formation of a complex between calmodulin and a canonical target peptide from skeletal muscle myosin light chain kinase measured by isothermal titration. The surprising lack of perturbation suggests that this probe group could be applied directly in many protein–protein binding interfaces. The infrared absorption bands for the probe groups reported many dramatic changes in the probes’ local environments as CaM went from apo- to calcium-saturated to target peptide-bound conditions, including large frequency shifts and a variety of line shapes from narrow (interpreted as a rigid and invariant local environment) to symmetric to broad and asymmetric (likely from multiple coexisting and dynamically exchanging structures). The fast intrinsic time scale of infrared spectroscopy means that the line shapes report directly on site-specific details of calmodulin’s variable structural distribution. Though quantitative interpretation of the probe line shapes depends on a direct connection between simulated ensembles and experimental data that does not yet exist, formation of such a connection to data such as that reported here would provide a new way to evaluate conformational ensembles from data that directly contains the structural distribution. The calmodulin probe sites developed here will also be useful in evaluating the binding mode of calmodulin with many uncharacterized regulatory targets.

Cryogenic positioning and alignment with micrometer precision in a magnetic resonance force microscope.

Aligning a microcantilever to an area of interest on a sample is a critical step in many scanning probe microscopy experiments, particularly those carried out on devices and rare, precious samples. We report a series of protocols that rapidly and reproducibly align a high-compliance microcantilever to a <10 μm sample feature under high vacuum and at cryogenic temperatures. The first set of protocols, applicable to a cantilever oscillating parallel to the sample surface, involve monitoring the cantilever resonance frequency while laterally scanning the tip to map the sample substrate through electrostatic interactions of the substrate with the cantilever. We demonstrate that when operating a cantilever a few micrometers from the sample surface, large shifts in the cantilever resonance frequency are present near the edges of a voltage-biased sample electrode. Surprisingly, these "edge-finder" frequency shifts are retained when the electrode is coated with a polymer film and a ∼10 nm thick metallic ground plane. The second series of methods, applicable to any scanning probe microscopy experiment, integrate a single-optical fiber to image line scans of the sample surface. The microscope modifications required for these methods are straightforward to implement, provide reliable micrometer-scale positioning, and decrease the experimental setup time from days to hours in a vacuum, cryogenic magnetic resonance force microscope.

In vivo characterization of brain ultrashort-T2 components.

Recent nuclear magnetic resonance and MRI studies have measured a fast-relaxing signal component with T2∗<1 ms in white matter and myelin extracts. In ex vivo studies, evidence suggests that a large fraction of this component directly arises from bound protons in the myelin phospholipid membranes. Based on these results, this ultrashort-T2 component in nervous tissue is a new potential imaging biomarker of myelination, which plays a critical role in neuronal signal conduction across the brain and loss or degradation of myelin is a key feature of many neurological disorders. The goal of this work was to characterize the relaxation times and frequency shifts of ultrashort-T2 components in the human brain. This required development of an ultrashort echo time relaxometry acquisition strategy and fitting procedure for robust measurements in the presence of ultrashort T2∗ relaxation times and large frequency shifts. We measured an ultrashort-T2 component in healthy volunteers with a median T2∗ between 0.5-0.7 ms at 3T and 0.2-0.3 ms at 7T as well as an approximately -3 ppm frequency shift from water. To our knowledge, this is the first time a chemical shift of the ultrashort-T2 brain component has been measured in vivo. This chemical shift, at around 1.7 ppm, is similar to the primary resonance of most lipids, indicating that much of the ultrashort-T2 component observed in vivo arises from bound protons in the myelin phospholipid membranes. Magn Reson Med 80:726-735, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Modes of Rapid Polygenic Adaptation.

Many experimental and field studies have shown that adaptation can occur very rapidly. Two qualitatively different modes of fast adaptation have been proposed: selective sweeps wherein large shifts in the allele frequencies occur at a few loci and evolution via small changes in the allele frequencies at many loci. Although the first process has been thoroughly investigated within the framework of population genetics, the latter is based on quantitative genetics and is much less understood. Here we summarize results from our recent theoretical studies of a quantitative genetic model of polygenic adaptation that makes explicit reference to population genetics to bridge the gap between the two frameworks. Our key results are that polygenic adaptation may be a rapid process and can proceed via subtle or dramatic changes in the allele frequency depending on the sizes of the phenotypic effects relative to a threshold value. We also discuss how the signals of polygenic selection may be detected in the genome. Although powerful methods are available to identify signatures of selective sweeps at loci controlling quantitative traits, the development of statistical tests for detecting small shifts of allele frequencies at quantitative trait loci is still in its infancy.

Observation of the Bloch-Siegert shift in a driven quantum-to-classical transition

We show that the counter-rotating terms of the dispersive qubit-cavity Rabi model can produce relatively large and nonmonotonic Bloch-Siegert shifts in the cavity frequency as the system is driven through a quantum-to-classical transition. Using a weak microwave probe tone, we demonstrate experimentally this effect by monitoring the resonance frequency of a microwave cavity coupled to a transmon and driven by a microwave field with varying power. In the weakly driven regime (quantum phase), the Bloch-Siegert shift appears as a small constant frequency shift, while for strong drive (classical phase) it presents an oscillatory behaviour as a function of the number of photons in the cavity. The experimental results are in agreement with numerical simulations based on the quasienergy spectrum.

Revealing the nonlinear response of a tunneling two-level system ensemble using coupled modes

Atomic sized two-level systems (TLSs) in amorphous dielectrics are known as a major source of loss in superconducting devices. In addition, individual TLS are known to induce large frequency shifts due to strong coupling to the devices. However, in the presence of a broad ensemble of TLSs these shifts are symmetrically canceled out and not observed in a typical single-tone spectroscopy experiment. We introduce a two-tone spectroscopy on the normal modes of a pair of coupled superconducting coplanar waveguide resonators to reveal this effect. Together with an appropriate saturation model this enables us to extract the average single-photon Rabi frequency of dominant TLSs to be $\Omega_0/2\pi \approx 79 $ kHz. At high photon numbers we observe an enhanced frequency shift due to nonlinear kinetic inductance when using the two-tone method and estimate the value of the nonlinear coefficient as $K/2\pi \approx -1\times 10^{-4}$ Hz/photon. Furthermore, the life-time of each resonance can be controlled (increased) by pumping of the other mode as demonstrated both experimentally and theoretically.

Guest Hydrogen Bond Dynamics and Interactions in the Metal–Organic Framework MIL-53(Al) Measured with Ultrafast Infrared Spectroscopy

MIL-53(Al) is among the most “flexible” metal–organic frameworks and significantly changes its structure when guest molecules are introduced into the framework’s pores. The guest molecules interact with μ2-OH, which is a hydroxyl group bridging two aluminums. This interaction is thought to play an important role in the adsorption of molecules into the pores. Here, we report infrared absorption, infrared pump–probe, and two-dimensional infrared spectroscopy on a deuterated bridging hydroxyl, μ2-OD, in MIL-53(Al) loaded with various guest molecules. Depending on guest, large vibrational frequency shifts, broadening of absorption band, enhancement of absorption coefficient, and acceleration of vibrational relaxation were observed, which are all signatures of hydrogen bonding interactions between the bridging hydroxyls and the guest. 2D IR spectroscopy reveals that the time evolution of the vibrational frequency occurs on multiple time scales: subpicosecond dynamics caused by localized hydrogen bond fluctuati...

Magnesium as a Novel UV Plasmonic Material for Fluorescence Decay Rate Engineering in Free Solution

We report modification of the ultraviolet (UV) fluorescence decay rate of p-terphenyl dye molecules by magnesium (Mg) nanoapertures in free solution, in comparison with aluminum (Al). Mg nanoapertures exhibit a lifetime reduction of up to ∼7.2×, which to our knowledge is the largest lifetime reduction of a UV fluorescence dye reported so far in the literature. In comparison, Al nanoapertures exhibit a lifetime reduction of ∼5.3×, exceeding the previously reported value ∼3.5× due to smaller aperture size employed here. Simulation results reveal large plasmon resonance frequency shifts between Mg and Al nanoapertures, contributing to different lifetime reductions, where average lifetime reductions of Mg nanoapertures are greater than those of Al nanoapertures with diameters smaller than 40 nm. The dependence of count rate per molecule (CRM) on aperture size and aperture undercut is also reported, revealing that CRM increases with increasing undercut.

Optical Frequency Shifter Employing a Brillouin-Assisted Filtering Technique

A new optical frequency shifter is presented. It is based on a double sideband suppressed carrier radio-frequency (RF) modulated optical signal into a Brillouin-assisted filter, which is formed by a Brillouin medium between a pair of optical circulators. The frequency shifting operation is realized by utilizing multiple stimulated Brillouin scattering gain and loss spectra to amplify one of the third-order sidebands but attenuate the other sidebands. The frequency shifter has a simple structure and a high frequency shifted to unwanted frequency component ratio. It also has the ability to realize a very large frequency shift, which is three times the input electrical driving signal frequency. The frequency shifter is experimentally demonstrated with the results showing a 32.53 GHz optical frequency shift of a continuous wave light at 1551.016 nm with over 34 dB difference between the wanted frequency shifted and unwanted frequency components.

Enhancement in CMOS-MEMS Resonator for High Sensitive Temperature Sensing

This paper presents the enhancement in frequency shift per Celsius for high-temperature sensitive applications of microresonators. Using materials with different coefficients of thermal expansion in a substrate and beam, larger axial load on fixed ends are demonstrated. This results in a larger frequency shift with the increase in the ambient temperature. An analytical model is presented that closely matches simulation and measurement results. The 120- $\mu \text{m}$ CMOS-MEMS fixed–fixed beam resonators, consisting of multiple metal, dielectric layers, and polysilicon layer, were designed and measured with a center frequency around 640 kHz. A sensitivity up to −2983 Hz/°C is achieved without sacrificing stiffness constant.

Nanoparticle-Modified Magnetic Vortex Dynamics

With a view toward ferromagnetic-resonance-mediated detection of magnetic nanoparticles, we use micromagnetic simulations to study how the stray magnetic field produced by a uniformly magnetized spherical magnetic nanoparticle can modify the vortex gyrotropic resonance. We also show how these modifications depend on the particle's position and size. For small particle sizes, a core confinement effect induced by interaction between the particle's highly localized out-of-plane stray field and the vortex core magnetization can induce large frequency shifts. However, the generation of large shifts via this mechanism relies on the core's trajectory being localized directly below the particle. For larger particles (which generate stronger but less localized stray fields), changes in the gyrotropic frequency result from a combination of wide-scale out-of-plane spin canting and in-plane-field-induced shifting of the vortex core within its anharmonic confining potential. Compared to confinement-driven frequency shifting, the generation of large frequency shifts ( ${\gtrsim }$ 10 MHz) via these latter mechanisms is less dependent on particle positioning and the core orbit radius. The use of large particles, thus, represents a more reliable sensing modality if the particles cannot be guaranteed to align centrally over the disk.

一种带有ICI自消除的多OFDM符号时变信道估计方法

高速移动环境下，由于多普勒频移增大，信道的时变性破坏了正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)系统子载波之间的正交性，从而产生子载波间干扰(Inter Carrier Interference, ICI)，导致系统性能严重下降。为了减少待估计量，通常采用基扩展模型(BEM)来近似模拟时变信道。为了提升性能，当信道的相干时间与发送码元的周期可相比拟的时候，本文采用多块(多个OFDM符号)。同时在使用导频符号对参数估计时，忽略了相邻非导频符号的ICI干扰，降低了整个时变信道下的估计准确性。因此我们通过分析子载波所产生的ICI系数变化特点，提出了一种带有ICI自消除的多OFDM符号时变信道估计方法，提高估计的准确性。但是由于基于多OFDM符号的信道估计性能在归一化多普勒频移较大时该方法成立条件不再满足，因此性能呈现明显的衰减，为了解决此问题，我们提出一种带有ICI自消除的自适应OFDM符号个数时变信道估计方法。仿真实验从误码率，归一化均方误差两方面分别验证了该方法的有效性。 In high-speed mobile environment, time-varying channel destroys the orthogonality between subcarriers of orthogonal frequency-division multiplexing (OFDM) systems, giving rise to in-ter-carrier interference (ICI), and degrading the performance of the systems. Basis expansion model (BEM) is usually used to approximate the time-varying channels to reduce the estimators. In order to improve performance, this paper adopts multi block (multiple OFDM symbols) when the coherent time of the channel variations and the symbols can be compared. However, when using pilot-symbol to parameter estimation, the ICI interference from near non-pilot-symbol is ignored, reducing its estimated accuracy of time-varying channel. And in this work the paper proposes a multiple OFDM symbols time-varying channel estimation method with ICI self-cancellation after analyzing the high correlation between subcarriers, improving the accuracy of estimation. But due to the condition of utilizing the multiple OFDM symbols channel estimation method is no longer met in large Doppler frequency shift, the performance of resulting channel estimation attenuates obviously. In order to solve this problem, we put forward a kind of adaptive OFDM symbol time-varying channel estimation method with the ICI self-cancellation. The simulation results show that the proposed method is effective from two aspects of error rate and normalized mean square error.

Transfer cavity scheme for stabilization of lattice laser in ytterbium lattice clock

For high performance clock, optical lattice is introduced to generate periodic trap for capturing neutral atoms through weak interactions. However, the strong trapping potential can bring a large AC Stark frequency shift due to imbalance shifts for the upper and lower energy levels of the clock transition. Fortunately, it is possible to find a specific “magic” wavelength for the lattice light, at which the first-order net AC Stark shift equals zero. To achieve high stability and accuracy of a neutral atomic optical clock, the frequency of the lattice laser must be stabilized and controlled to a certain level around magic wavelength to reduce this shift.#br#In this paper, we report that the frequency of lattice laser is stabilized and linewidth is controlled below 1 MHz with transfer cavity scheme for ytterbium (Yb) clock. A confocal invar transfer cavity mounted in an aluminum chamber is locked through the Pound-Drever-Hall (PDH) method to a 780 nm diode laser stabilized with modulation transfer spectroscopy of rubidium D2 transition. It is then used as the locking reference for the lattice laser. This cavity has a free spectral range of 375 MHz, as well as fineness of 236 at 780 nm, and 341 at 759 nm. Because neither of the wavelengths of 759 nm and 780 nm is separated enough to use optical filter, they are coupled into the cavity with transmission and reflection way respectively, and the two PDH modulation frequencies are chosen differently to avoid possible interference.#br#The stabilization of the 759 nm lattice laser on transfer cavity can stay on for over 12 hours without escaping or mode hopping. To estimate the locking performance of the system, a beat note with a hydrogen maser-locked optical frequency comb is recorded through a frequency counter at 10 ms gate time for over 3 hours. This beat note shows that the frequency fluctuation is in a range of 10 kHz corresponding to a stability of 2×10-11 level with 0.1 s averaging time, but goes up to 150 kHz corresponding to a stability of 3.6×10-10 at 164 s averaging time. The long-term drift can be the result of air pressure fluctuation on the transfer cavity, or the bad stability of the optical comb in the measurement process. However, current locking performance is still enough for the requirement of 10-17 clock uncertainty.#br#In conclusion, we succeed in realizing frequency stabilization and control for the lattice laser of Yb clock with the transfer cavity scheme. The result shows that the short-term stability is around 10-11 level, though a mid-long-term drift exists. However, the stability of 3.6×10-10 over 164 s can still promise a 10-17 uncertainty for the Yb clock. And, it can be reduced if the averaging time is long enough. The work can be further improved by installing the transfer cavity into vacuum housing for better stability in future.

Highly Sensitive SH-SAW Resonator with SiO2 trenches for Biosensing Application

The paper presents three dimensional finite element simulation of a sensitive shear-horizontal surface acoustic wave device for biosensing application. The resonator consisting of 36°-YX LiTaO3 substrate with SiO2 trenches generates a shear-horizontal standing wave. Eigenmode study and frequency response are used to calculate displacements, admittance and electromechanical coupling coefficient of the device. For a given mode, the coupling coefficient of the device increases with trench height to a maximum of about 7% and then starts to decrease till next higher order mode becomes dominant. The trenches not only serve as guiding layer to keep the energy of the wave at the surface but also cause coupled resonance leading to increase in resonance frequency and average stress at the contact area between trench and substrate. Mass loading of resonator is simulated by applying the equivalent surface mass density of double stranded DNA of length 50 base pairs uniformly over the surface area of trenches. Close to the resonant height of trenches, mass loading causes a large frequency shift making the device a highly sensitive biosensing platform.

Observation of Collective Coupling between an Engineered Ensemble of Macroscopic Artificial Atoms and a Superconducting Resonator.

The hybridization of distinct quantum systems is now seen as an effective way to engineer the properties of an entire system leading to applications in quantum metamaterials, quantum simulation, and quantum metrology. Recent improvements in both fabrication techniques and qubit design have allowed the community to consider coupling large ensembles of artificial atoms, such as superconducting qubits, to a resonator. Here, we demonstrate the coherent coupling between a microwave resonator and a macroscopic ensemble composed of several thousand superconducting flux qubits, where we observe a large dispersive frequency shift in the spectrum of 250MHz. We achieve the large dispersive shift with a collective enhancement of the coupling strength between the resonator and qubits. These results represent the largest number of coupled superconducting qubits realized so far.

Anomalous time delays and quantum weak measurements in optical micro-resonators.

Quantum weak measurements, wavepacket shifts and optical vortices are universal wave phenomena, which originate from fine interference of multiple plane waves. These effects have attracted considerable attention in both classical and quantum wave systems. Here we report on a phenomenon that brings together all the above topics in a simple one-dimensional scalar wave system. We consider inelastic scattering of Gaussian wave packets with parameters close to a zero of the complex scattering coefficient. We demonstrate that the scattered wave packets experience anomalously large time and frequency shifts in such near-zero scattering. These shifts reveal close analogies with the Goos–Hänchen beam shifts and quantum weak measurements of the momentum in a vortex wavefunction. We verify our general theory by an optical experiment using the near-zero transmission (near-critical coupling) of Gaussian pulses propagating through a nano-fibre with a side-coupled toroidal micro-resonator. Measurements demonstrate the amplification of the time delays from the typical inverse-resonator-linewidth scale to the pulse-duration scale.

Biosensor surface attachment of the ovarian cancer biomarker HSP10 via His-tag modification

Herein, we describe a new protocol for the silane-based surface modification of quartz substrates for the immobilization of hexa-histidine-tagged heat shock protein 10. This molecule is an attractive biomarker for the detection of ovarian cancer, particularly for possible early-stage diagnosis. The surface chemistry we have described is used for a study of the interaction between the protein and a novel DNA aptamer via an in-house built acoustic wave sensing platform. Quartz discs were modified with a mixed trichlorosilane adlayer and functionalized with a nickel-NTAL moiety to allow for immobilization of the protein in a correctly-oriented fashion. All layers were characterized by x-ray photoelectron spectroscopy to show successful layer modification. Detection of binding in phosphate buffered saline was determined using the EMPAS, operating at a fundamental frequency of 940MHz. Results regarding the specific binding of the DNA aptamer to the surface-immobilized protein exhibited a significantly smaller signal compared to surfaces without protein, which comparatively yielded much larger frequency shifts. The smaller shift in frequency is attributed to the rigidification of the bulk layer upon interaction between probe and ligand as the overwhelming factor. This rigidification is counteracted by mass loading effects, in which a balance between these two factors is what contributes to the overall smaller frequency shift. Without the binding interaction, the bulk layer does not rigidify, resulting in mass loading being the main contributor to signal, and thus a large frequency shift is seen.

Raman spectroscopy of KxCo2−ySe2 single crystals near the ferromagnet–paramagnet transition

Polarized Raman scattering spectra of the KxCo2−ySe2 single crystals reveal the presence of two phonon modes, assigned as of the A1g and B1g symmetry. The absence of additional modes excludes the possibility of vacancy ordering, unlike in KxFe2−ySe2. The ferromagnetic (FM) phase transition at K leaves a clear fingerprint on the temperature dependence of the Raman mode energy and linewidth. For the temperature dependence looks conventional, driven by the thermal expansion and anharmonicity. The Raman modes are rather broad due to the electron–phonon coupling increased by the disorder and spin fluctuation effects. In the FM phase the phonon frequency of both modes increases, while an opposite trend is seen in their linewidth: the A1g mode narrows in the FM phase, whereas the B1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B1g mode is due to the coupling of spin fluctuations and vibration. Our density functional theory (DFT) calculations for the phonon frequencies agree rather well with the Raman measurements, with some discrepancy being expected since the DFT calculations neglect the spin fluctuations.

Mass spectral decomposition mechanisms of RDX isomers upon electron attachment and electron ionisation: a DFT study of normal mode activation incorporating Duschinsky rotations

ABSTRACTThe excited normal modes of RDX isomers upon loss and gain of an electron were calculated using DFT methods. Isomerisation and N−N bond dissociation accompany the cation and anion formation, respectively, resulting in rather large (0.03–2.5 eV) reorganisation energies, frequency shifts and mode mixing. All active vibrations are found to be anharmonic. The suggested mass spectral fragmentation products for the cations along the S0 surface are 42, 60, 74, 84, 120, 130, 148 and 176 amu, in agreement with earlier mass spectrometry studies. For anions, N−N bond dissociation is common and dominant for all isomers with frequency shifts being more significant than mode mixing.