Experimental investigation of inter-element isolation in a medical array transducer at various manufacturing stages

This work presents the experimental investigation of vibration maps of a linear array transducer with 192 piezoelements by means of a laser Doppler vibrometer at various manufacturing finishing steps in air and in water. Over the years, many researchers have investigated cross-coupling in fabricated prototypes but not in arrays at various manufacturing stages. Only the central element of the array was driven at its working frequency of 5 MHz. The experimental results showed that the contributions of cross-coupling depend on the elements of the acoustic stack: Lead Zirconate Titanate (PZT), kerf, filler, matching layer, and lens. The oscillation amplitudes spanned from (6 ± 38%) nm to (110 ± 40%) nm when the energized element was tested in air and from (6 ± 57%) nm to (80 ± 67%) nm when measurements were obtained under water. The best inter-element isolation of -22 dB was measured in air after cutting the kerfs, whereas the poorest isolation was -2 dB under water with an acoustic lens (complete acoustic stack). The vibration pattern in water showed a higher standard deviation on the displacement measurements than the one obtained in air, due to the influence of acousto-optic interactions. The amount increased to 30% in water, as estimated by a comparison with the measurements in air. This work describes a valuable method for manufacturers to investigate the correspondence between the manufacturing process and the quantitative evaluations of the resulting effects

O(N)O(N) fluctuations and lattice distortions in 1-dimensional systems

Statistical mechanics harmonizes mechanical and thermodynamical quantities, via the notion of local thermodynamic equilibrium (LTE). In absence of external drivings, LTE becomes equilibrium tout court, and states are characterized by several thermodynamic quantities, each of which is associated with negligibly fluctuating microscopic properties. Under small driving and LTE, locally conserved quantities are transported as prescribed by linear hydrodynamic laws, in which the local material properties of the system are represented by the transport coefficients. In 1-dimensional systems, on the other hand, the transport coefficients often appear to depend on the global state, rather than on the local state of the system at hand. We interpret these facts within the framework of boundary driven 1-dimensional Lennard-Jones chains of $N$ oscillators, observing that they experience non-negligible $O(N)$ lattice distortions and fluctuations. This implies that standard hydrodynamics and certain expressions of energy flow do not apply in these cases. One possible modification of the energy flow is considered.Comment: 8 pages, 7 figure

Revealing Hidden Vibration Polariton Interactions by 2D IR Spectroscopy

We report the first experimental two-dimensional infrared (2D IR) spectra of novel molecular photonic excitations - vibrational-polaritons. The application of advanced 2D IR spectroscopy onto novel vibrational-polariton challenges and advances our understanding in both fields. From spectroscopy aspect, 2D IR spectra of polaritons differ drastically from free uncoupled molecules; from vibrational-polariton aspects, 2D IR uniquely resolves hybrid light-matter polariton excitations and unexpected dark states in a state-selective manner and revealed hidden interactions between them. Moreover, 2D IR signals highlight the role of vibrational anharmonicities in generating non-linear signals. To further advance our knowledge on 2D IR of vibrational polaritons, we develop a new quantum-mechanical model incorporating the effects of both nuclear and electrical anharmonicities on vibrational-polaritons and their 2D IR signals. This work reveals polariton physics that is difficult or impossible to probe with traditional linear spectroscopy and lays the foundation for investigating new non-linear optics and chemistry of molecular vibrational-polaritons

Qubit coherence decay down to threshold: influence of substrate dimensions

Keeping single-qubit quantum coherence above some threshold value not far below unity is a prerequisite for fault-tolerant quantum error correction (QEC). We study the initial dephasing of solid-state qubits in the independent-boson model, which describes well recent experiments on quantum dot (QD) excitons both in bulk and in substrates of reduced geometry such as nanotubes. Using explicit expressions for the exact coherence dynamics, a minimal QEC rate is identified in terms of the error threshold, temperature, and qubit-environment coupling strength. This allows us to systematically study the benefit of a current trend towards substrates with reduced dimensions.Comment: 4 pages, 4 figure

Analytical prediction of stability limit in turning operations

Unstable cutting due to chatter vibrations is one of the most important problems during metal cutting operations. Chatter can be a limitation for productivity and surface quality in turning operations, especially when long and slender tools and parts are involved. In this study, an analytical stability method for turning process is presented. The model takes the cutting geometry into consideration, and proposes a new solution procedure for the dynamic chip thickness at the insert nose. The analytically calculated absolute stable depth of cuts are compared with the chatter test results, and a good agreement is observed

Optical spectroscopic study of the interplay of spin and charge in NaV2O5

We investigate the temperature dependent optical properties of NaV2O5, in the energy range 4meV-4eV. The symmetry of the system is discussed on the basis of infrared phonon spectra. By analyzing the optically allowed phonons at temperatures below and above the phase transition, we conclude that a second-order change to a larger unit cell takes place below 34 K, with a fluctuation regime extending over a broad temperature range. In the high temperature undistorted phase, we find good agreement with the recently proposed centrosymmetric space group Pmmn. On the other hand, the detailed analysis of the electronic excitations detected in the optical conductivity, provides direct evidence for a charge disproportionated electronic ground-state, at least on a locale scale: A consistent interpretation of both structural and optical conductivity data requires an asymmetrical charge distribution on each rung, without any long range order. We show that, because of the locally broken symmetry, spin-flip excitations carry a finite electric dipole moment, which is responsible for the detection of direct two-magnon optical absorption processes for E parallel to the a axis. The charged-magnon model, developed to interpret the optical conductivity of NaV2O5, is described in detail, and its relevance to other strongly correlated electron systems, where the interplay of spin and charge plays a crucial role in determining the low energy electrodynamics, is discussed.Comment: Revtex, 19 pages, 16 postscript pictures embedded in the text, submitted to PRB. Find more stuff at http://www.stanford.edu/~damascel/andreaphd.html or http://www.ub.rug.nl/eldoc/dis/science/a.damascelli

Coherent Phonons in Carbon Nanotubes and Graphene

We review recent studies of coherent phonons (CPs) corresponding to the radial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs) and graphene. Because of the bandgap-diameter relationship, RBM-CPs cause bandgap oscillations in SWCNTs, modulating interband transitions at terahertz frequencies. Interband resonances enhance CP signals, allowing for chirality determination. Using pulse shaping, one can selectively excite speci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit temperature-dependent dephasing via interaction with RBM phonons. Our microscopic theory derives a driven oscillator equation with a density-dependent driving term, which correctly predicts CP trends within and between (2n+m) families. We also find that the diameter can initially increase or decrease. Finally, we theoretically study the radial breathing like mode in graphene nanoribbons. For excitation near the absorption edge, the driving term is much larger for zigzag nanoribbons. We also explain how the armchair nanoribbon width changes in response to laser excitation.Comment: 48 pages, 41 figure

Analytical stability models for turning and boring operations

In this paper an analytical model for stability limit predictions in turning and boring operations is proposed. The multi-dimensional model includes the 3D geometry of the processes. In addition a model for the chip thickness at the insert nose radius is also proposed to observe the effect of the insert nose radius on the chatter stability limit. Chatter experiments are conducted for both turning and boring in order to compare with analytical results and good agreement is observed