AC Flow Research Articles

Separation of tumor cells with dielectrophoresis-based microfluidic chip

The present work demonstrates the use of a dielectrophoretic lab-on-a-chip device in effectively separating different cancer cells of epithelial origin for application in circulating tumor cell (CTC) identification. This study uses dielectrophoresis (DEP) to distinguish and separate MCF-7 human breast cancer cells from HCT-116 colorectal cancer cells. The DEP responses for each cell type were measured against AC electrical frequency changes in solutions of varying conductivities. Increasing the conductivity of the suspension directly correlated with an increasing frequency value for the first cross-over (no DEP force) point in the DEP spectra. Differences in the cross-over frequency for each cell type were leveraged to determine a frequency at which the two types of cell could be separated through DEP forces. Under a particular medium conductivity, different types of cells could have different DEP behaviors in a very narrow AC frequency band, demonstrating a high specificity of DEP. Using a microfluidic DEP sorter with optically transparent electrodes, MCF-7 and HCT-116 cells were successfully separated from each other under a 3.2 MHz frequency in a 0.1X PBS solution. Further experiments were conducted to characterize the separation efficiency (enrichment factor) by changing experimental parameters (AC frequency, voltage, and flow rate). This work has shown the high specificity of the described DEP cell sorter for distinguishing cells with similar characteristics for potential diagnostic applications through CTC enrichment.

Two-parameter flow ofσxx(ω)-σxy(ω)for the graphene quantum Hall system in the ac regime

Flow diagram of $(\sigma_{xx}, \sigma_{xy})$ in finite-frequency ($\omega$) regime is numerically studied for graphene quantum Hall effect (QHE) system. The ac flow diagrams turn out to show qualitatively similar behavior as the dc flow diagrams, which can be understood that the dynamical length scale determined by the frequency poses a relevant cutoff for the renormalization flow. Then the two parameter flow is discussed in terms of the dynamical scaling theory. We also discuss the larger-$\omega$ regime which exhibits classical flows driven by the raw frequency $\omega$.

Dynamical Scaling of the Critical Velocity for the Onset of Turbulence in Oscillatory Superflows

The critical velocity v_c for the onset of turbulence in oscillatory flows of superfluid helium is known to depend on the oscillation frequency omega, namely v_c ~ sqrt(kappa*omega) where kappa is the circulation quantum. Only the numerical prefactor may have some geometry dependence. This universal behaviour was described earlier qualitatively either by employing the superfluid Reynolds number or by extending known dc vortex dynamics to ac flow. In our present work we emphasize that v_c(omega) ~ sqrt(omega) can also be derived rigorously by means of dynamical scaling of equations of vortex dynamics as pointed out by Kotsubo and Swift already two decades ago.

Anticipatory and carry-over laryngeal coarticulation in 5-year-old children and adults.

Many studies have compared the time course of coarticulation between children and adults. Most of this work has assessed supralaryngeal aspects of articulation. However, laryngeal coarticulation also occurs, as evident in measures of fundamental frequency (f0) and voice source features in vowels flanking voiceless consonants. Moreover, most developmental work has focused on anticipatory coarticulation, which is thought to reflect planning. In contrast, carryover coarticulation is thought to result mainly from articulatory inertia. Thus, the two forms of coarticulation may show different developmental time courses. This work evaluates laryngeal coarticulation in typically developing 5-year-old English-speaking children and adult females via measures of oral airflow. Speakers produced approximately 25 repetitions each of intervocalic /b p h/, with the target consonant initiating a stressed syllable. From the airflow signal, pulse-by-pulse measures were made of the smoothed airflow (DC flow), the pulse amplitude (AC flow), and f0 before and after the target consonants. Previous analyzes of a subset of these data indicated that carryover coarticulation in children was highly variable from token to token, complicating age comparisons based on average measures. Of particular interest here is whether the degree of coarticulatory variability differs depending on direction (anticipatory versus carryover).

Optimal Capacity Expansion in Electric Power Subtransmission Networks

A procedure is proposed to determine where and when to increase the capacity of lines and transformers in a power subtransmission network. The expansion plan must minimize cost while supplying the demand for energy over a time horizon, keeping the quality and reliability standards of the network and minimizing the impact over the environment. The procedure is iterative and takes into account AC flows, reliability analysis, different scenarios, demand uncertainty, discrete investment costs, voltage constraints, capacity, and power factor. A significant contribution of this procedure is that, along with the expansion plan, it considers the optimization of the operation, specifically the movement of transformer taps and the location and sizing of reactive banks. This allows significantly reducing or delaying the investment, thus reducing its present value. The approach ensures convergence when computing the power flows and allows making an analysis of the effects of distributed generation and, if necessary, ...

Salivary flow rates measured during radiation therapy in head and neck cancer patients: A pilot study assessing salivary sediment formation

Xerostomia often occurs in patients being managed for head and neck cancer who receive radiation therapy. Although accurate salivary sampling can be therapeutically important to measure during radiation, sampling errors can occur because of salivary sediments. Determining the impact that salivary sediments have on measured salivary flow rates during radiation is important for management of patients. The purpose of this study was to assess the magnitude of error associated with the inclusion of nonsalivary components (sediment) in the calculation of whole stimulated saliva flow rates prior to and during radiation therapy (SS and SSR) in patients with head and neck cancer. Whole paraffin-stimulated saliva was collected in large-mouth centrifuge tubes from 20 patients with head and neck cancer prior to and during the third week of radiation therapy. Gravimetric methods were used to calculate the flow rates at g/5 min. After centrifugation, supernatant saliva was removed and the sediment was oven-dried to remove residual moisture. Sediment weight was subtracted from the original weight of saliva specimens and flow rates were recalculated. Means and standard deviations were determined and flow rate differences before (BC) and after (AC) sediment correction were evaluated statistically with the paired t test (alpha=.05). A nonparametric analysis of the flow rate data with the Wilcoxon matched-pairs signed-ranks test was also used to examine the magnitude and direction of the intrapair (BC-AC) differences (alpha=.05). On average, salivary sediment contributed less than 1% of the total uncorrected weight of saliva prior to radiation therapy. In specimens collected during radiation therapy, sediment contributed an average of 14% of the total uncorrected weight and as high as 95.4% in 1 patient. Sediment percentages were 20% and higher in 4 patients. In the Wilcoxon analysis, 19 out of 20 paired BC and AC flow rates were higher in the BC group in the SS and SSR samples. The error associated with the inclusion of salivary sediment in the calculation of saliva flow rates prior to radiation treatment was small, but statistically significant. The magnitude of the sediment effect was more pronounced in specimens taken during radiotherapy and was significant, as determined by the Wilcoxon test, but the mean paired differences were not significantly different according to the t test.

Impact of in-plane currents on magnetoresistance properties of an exchange-biased spin valve with an insulating antiferromagnetic layer

The impact of in-plane alternating currents on the exchange bias, resistance, and magnetoresistance of a ${\mathrm{Co}}_{85}{\mathrm{Fe}}_{15}∕{\mathrm{Ni}}_{0.85}{\mathrm{Co}}_{0.15}\mathrm{O}∕{\mathrm{Co}}_{85}{\mathrm{Fe}}_{15}∕\mathrm{Cu}∕{\mathrm{Co}}_{85}{\mathrm{Fe}}_{15}$ spin valve is studied. With increasing current, the resistance is increased while the maximum magnetoresistance ratio decreases. Noticeably, the reversal field of the pinned layer is systematically suppressed in both field sweeping directions. Since ${\mathrm{Ni}}_{0.85}{\mathrm{Co}}_{0.15}\mathrm{O}$ is a good insulator, it is expected that the ac flows only in the ${\mathrm{Co}}_{85}{\mathrm{Fe}}_{15}∕\mathrm{Cu}∕{\mathrm{Co}}_{85}{\mathrm{Fe}}_{15}$ top layers, thus ruling out any presence of spin-transfer torque acting on the spins in the antiferromagnetic layer. Instead, our measurements show clear evidence of the influence of Joule heating caused by the current. Moreover, results from temperature-dependent measurements very much resemble those of the current dependence, which indicates that the effect of Joule heating plays a major role in the current-in-plane spin-valve configurations. The results also suggest that spin-transfer torques between ferromagnetic layers might still exist and compete with the exchange bias at sufficiently high currents.

Rate Measurements of the Hydrolysis of Complex Organic Macromolecules in Cold Aqueous Solutions: Implications for Prebiotic Chemistry on the Early Earth and Titan

Organic macromolecules ("complex tholins") were synthesized from a 0.95 N(2)/0.05 CH(4) atmosphere in a high-voltage AC flow discharge reactor. When placed in liquid water, specific water soluble compounds in the macromolecules demonstrated Arrhenius type first order kinetics between 273 and 313 K and produced oxygenated organic species with activation energies in the range of approximately 60+/-10 kJ mol(-1). These reactions displayed half lives between 0.3 and 17 days at 273 K. Oxygen incorporation into such materials--a necessary step toward the formation of biological molecules--is therefore fast compared to processes that occur on geologic timescales, which include the freezing of impact melt pools and possible cryovolcanic sites on Saturn's organic-rich moon Titan.

Design and Characterization of Artificial Haircell Sensor for Flow Sensing With Ultrahigh Velocity and Angular Sensitivity

We report the development of an artificial hair cell (AHC) sensor with design inspired by biological hair cells. The sensor consists of a silicon cantilever beam with a high-aspect-ratio cilium attached at the distal end. Sensing is based on silicon piezoresistive strain gauge at the base of the cantilever. The cilium is made of photodefinable SU-8 epoxy and can be up to 700-mum tall. In this paper, we focus on flow-sensing applications. We have characterized the performance of the AHC sensor both in water and in air. For underwater applications, we have characterized the sensor under two flow conditions: steady-state laminar flow (dc flow) and oscillatory flow (ac flow). The detection limit of the sensor under ac flow in water is experimentally established to be below 1 mm/s. A best case angular resolution of 2.16deg is also achieved for the sensor's yaw response in air.

Quantum Turbulence Generated and Detected by a Vibrating Quartz Fork

Flow due to a commercially available vibrating quartz fork is studied in gaseous helium, He I, He II and 3He–B, over a wide range of temperatures and pressures. On increasing the driving force, the flow changes in character from laminar (characterized by a linear velocity versus drive dependence) to turbulent (characterized by a square root velocity versus drive dependence). In classical fluids, we characterize this transition by a critical Reynolds number, Re c =U cr δ/ν, where U cr is the critical velocity, ν stands for the kinematic viscosity, $\delta=\sqrt{2\nu/\omega}$ is the viscous penetration depth and ω is the angular frequency of oscillations. U cr of order 10 cm/s observed in He II and 1 mm/s in 3He–B agree with those found with other vibrating objects such as spheres, wires and grids, as well as with available numerical simulations of vortex motion in an applied ac flow.

The Transport Characteristics and the Self-field Distribution for High-Tc Superconductor with Neighboring Magnetic Materials

Many high-Tc superconducting (HTS) tape manufactures make an effort to improve the transport characteristics of HTS tapes. When AC or DC current flows in the HTS tape, AC or DC magnetic self-fields are induced around the conductor by the current and these self-fields affect on the AC loss and the critical current like the transport characteristics of HTS tapes. The spatial distribution and magnitude of the self-field are variable due to the neighboring materials on the HTS tape. In this paper, the relation between the transport characteristics and the self-field distribution of HTS tapes with paralleled ferromagnetic material (Ni tape) and/or diamagnetic material (BSCCO tape) is experimentally investigated. The self-fields according to the DC and AC transport currents were measured by hall probe with axial and radial magnetic field components. The critical currents of HTS tapes with paralleled the Ni tape are slightly decreased and the transport current losses markedly increased. However, the critical currents and transport current losses of HTS tapes with paralleled BSCCO tape showed more improved performance than those of single HTS tape. We explain these results using the change of the spatial distribution and magnitude of self-field on HTS tapes by the neighboring magnetic materials.

OP04.15: Nomograms of fetal intrauterine shunts

To generate nomograms for the blood flow velocity waveforms of central fetal intrauterine shunts Foramen Ovale (FO) and Ductus Arteriosus (DA). Data has been extracted from an ongoing, prospective longitudinal observational study of uteroplacental and fetal circulation. After an early dating scan to confirm gestational age, 155 women with singleton pregnancies were scanned serially from 16 weeks onwards at 4 weekly intervals till 24 weeks and two weekly intervals thereafter, till 38 weeks. Congenital anomalies were excluded. Echocardiographic studies of FO and DA flow velocity waveforms were performed. Other serial measurements for the trial included biometric measurements BPD, HC, AC, FL, AFI and Doppler flow velocity waveforms of Umbilical Artery, Middle Cerebral artery, Ductus Venosus and Uterine arteries. Patients with adverse outcomes were excluded and all the women with normal outcomes were included for data analysis. Every two gestational weeks patients were grouped and for these groups, the 5th, 50th and 95th percentiles were calculated for the FO, and DA Peak systolic velocity (PSV) and Pulsatility Index (PI). Gestation—specific reference ranges were constructed for the fetal intrauterine shunts. In normal pregnancies, PI of FO decreased and PI of DA was relatively constant with advancing gestation. However, the PSV of FO and DA increased linearly with gestational age. Reference ranges for fetal central intrauterine shunts have been established which may enhance our understanding of fetal compromise and aid in evaluating management of complications like fetal growth restriction as well as congenital cardiac malformations.

Alternating current flow in internally flawed conductors: A tomographic analysis

The alternating current potential drop technique is a nondestructive testing method that is mostly applied to estimate the depth of surface breaking flaws (e.g., cracks) in metallic conductors. When the flaw is hidden (internal or bottom cracks), other techniques (e.g., radiographic) must be used, which may only provide limited information on the location and dimensions of the hidden flaw. This work presents a detailed numerical analysis of ac flow in internally flawed conductors. The results can be used to reveal and estimate the dimensions and location of hidden flaws.

Characteristics of phonation in women who produce voiced versus voiceless /h/

Production of the consonant /h/ typically involves a vocal-fold abduction gesture. Although /h/ is traditionally described as voiceless in English, voiced allophones also occur. Our recent work has described the phonatory behavior of women who produce a mixture of voiced and voiceless /h/; our results suggested speaker-specific patterns of the factors that lead to devoicing. This study characterizes the behavior of normal women who produce exclusively voiced /h/ and compares it to those who produced both voiced and voiceless /h/. Measures of baseline (dc) airflow are used as an index of abduction degree; peak intraoral pressures during adjacent /p/ closures provide a measure of subglottal pressure; and pulse-by-pulse measures are made of f0 and pulse amplitude (ac flow) around the /h/ abduction gesture. Multidimensional analyses are carried out within speakers to determine how these vocal parameters are related. We expect that women who produce only voiced /h/ will differ from those who devoice some /h/ productions in the parameters that facilitate phonation, such as higher subglottal pressures, smaller abduction degrees, and reduced vocal-fold tension as reflected in f0 measures. Based on our previous findings, however, we also expect individual variation in the phonatory settings that produce voiced /h/. [Work supported by NIH.]

Averaging analysis of periodically forced fluid networks

For a lumped parameter model of a flow network driven by a periodic generator, we apply averaging to find an approximate solution and analyze its stability. The approximate solution has three parts: mean flow due to the resistive effects of branches, a time-periodic part due to “inductive” effects, and a mean flow average correction due to the interaction of nonlinear and time varying effects. We present an example that may explain the scenario leading to venous diseases. It is shown that the widening of a branch in a venous network leads to an increase in the AC flow and a decrease in the DC flow through that branch, thus increasing the stress on venous valves, and consequently leading to a further increase in the effective width of the vein.

Analysis of levels of support and resonance demonstrated by an elite singing teacher

This was a study of levels of singing expertise demonstrated by an elite operatic singer and teacher. This approach may prove advantageous because the teacher demonstrates what he thinks is important, not what the nonsinging scientist thinks should be important. Two pedagogical sequences were studied: (1) the location of support—glottis (poor), chest (better), abdomen (best); (2) locations of resonance—hard palate/straight tone (poor), mouth (better), sinus/head (best). Measures were obtained for a single frequency (196 Hz), the vowel /ae/, and for mezzo‐forte loudness using the /pae pae pae/ technique. Sequence differences: The support sequence was characterized by formant frequency lowering suggestive of vocal tract lengthening. The resonance sequence was characterized by flow (AC, mean flow) and abduction increases. Sequence similarities: The best locations had the widest F2 bandwidths. The better and best locations had the largest dB difference between F2 and F3. Although acoustic power increased through the sequences, the acoustic efficiency was not a discriminating factor. Open and speed quotients were not differentiating. The flow resistance was highest and aerodynamic power the lowest for the first of each sequence. Combined data: The maximum flow declination rate correlated highly with the AC flow (r=−0.92) and SPL (r=0.901).

Normalized amplitude quotient for parametrization of the glottal flow.

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.

Dynamic Extremes of Voice in the Light of Time Domain Parameters Extracted from the Amplitude Features of Glottal Flow and Its Derivative

In the first part of the study, the subjects (4 females, 4 males) produced sustained breathy, normal and pressed types of phonation. The maximum AC flow (f_ac) and the negative peak amplitude (d_min) of the first derivative of the glottal flow were extracted from glottal volume velocity waveforms estimated by inverse filtering. The ratio between f_ac and d_min (amplitude quotient, AQ), which gives an estimate of the closing time of the glottal flow, and its normalised version (NAQ) were computed. The NAQ values correlated strongly with the closing quotient of glottal flow. In the second part of the study, the aim was to investigate the dynamic extremes of the human voice in terms of F₀, SPL, f_ac, d_min, AQ and NAQ as well as the intraoral pressure (p) used for subglottal pressure estimation. Eleven normal subjects (5 females, 6 males) participated in this experiment. The subjects started with the production of soft phonation (approximately 55 dB at 40 cm) and increased their vocal intensity at 5-dB steps up to the level of 105 dB. At the analysis stage, the voice samples were divided into three categories: soft (<70 dB), normal (70–90 dB) and loud (>90 dB). In soft and normal phonation, intensity change was correlated with changes in the shape of the glottal flow waveform, whereas the loud voice samples showed a large increase in F₀ and p values. At the loudest extreme, d_min approached its maximum and AQ its minimum values and NAQ started to rise. In terms of the NAQ values of stressed syllables, the type of phonation was breathy in the soft intensity category, whereas in the normal and loud intensity categories it was within the range of the pressed type of phonation of sustained phonation samples.

The collection of peripheral blood stem cells (PBSC) from two paediatric patients weighing under 10 kg on the Cobe Spectra v-6

Two children with Stage IV neuroblastoma received the Kushner protocol and Lenograstim 5 mcg/kg/day from Day 5 until completion of collections. Child 1, female, was collected after cycle 6, at 27 months old, weighing 9.2 kg and 80 cm in height. The second child, male, was collected after cycle 4, at 19 months old, 10 kg and 80 cm in height. All procedures were performed on the Cobe Spectra cell separator using ABO compatible packed red cells to prime the machine. Venous access was achieved via 11F Vascaths that were inserted under general anaesthetic. The first collection used the autoPBSC program but, due to an inability to satisfactorily correct a very low interface, all subsequent procedures were performed on the MNC program. We used 80 ml/kg to calculate their total blood volume (TBV) as the Cobe Spectra uses an adult algorthium that is less accurate for paediatric cases. We aimed to process 3–4 TBV, the inlet flow rate was 2 ml/kg, the collect rate 0.8 ml/min, with a total collect volume between 10% and 12% of TBV. Both children were supported during the procedure with calcium chloride infusions to prevent citrate toxicity. The Cobe Spectra requires an AC pump speed of greater than 1 ml/min for continuous adequate anti-coagulation. After programming the Cobe Spectra with the patient data and setting the AC:Inlet at 25:1, the AC flow rate was less than the required 1 ml/min. To overcome this problem, heparin was administered as a loading dose of 75 units/kg 30 min prior to procedure commencement and then followed by a low dose heparin infusion 10–15 units/kg/h (500 units/kg in 50 ml at 1 ml/h). Collections commenced when white cell count was greater than 4×109/l (Day post Chemotherapy Day 15 [Child 1], Day 17 [Child 2]). Sedation was not required and procedures were well tolerated. The median procedure time was 135 min (130–150) with a median TBVs processed of 3.3 (3–3.47). Target CD34 was 2–3×106/kg based on current weight. Collection results are shown in Table 1.

Control of DC gas flow in a single-stage double-inlet pulse tube cooler

The use of double-inlet mode in the pulse tube cooler opens up a possibility of DC gas flow circulating around the regenerator and pulse tube. Numerical analysis shows that effects of DC flow in a single-stage pulse tube cooler are different in some aspects from that in a 4 K pulse tube cooler. For highest cooler efficiency, DC flow should be compensated to a small value, i.e. DC flow over average AC flow at regenerator inlet should be in the range −0.0013 to +0.00016. Dual valves with reversed asymmetric geometries were used for the double-inlet bypass to control the DC flow in this paper. The experiment, performed in a single-stage double-inlet pulse tube cooler, verified that the cooler performance can be significantly improved by precisely controlling the DC flow.