Multiple Thermal Cycles Research Articles

A Single-Step Digital Nucleic Acid Amplification Platform by Digital Plasma Separation on a Chip

Quantitative nucleic acid detection is the future for precision molecular medicine. However, multiple sample preparation steps and thermal heat cycles of PCR are necessary for nucleic acid (NA) analysis. We developed a single-step isothermal digital NA amplification microfluidic platform by a technique termed digital plasma separation. We invented an innovative biophysical microcliff design that allows the removal of blood cells based on inertia; it can skim plasma into 224 wells (100nl/well) in one-step (>99% separation efficiency for 6μm particles). By separating the blood cells that obstruct optical detection, the microcliff design enabled quantitative DNA detection via an isothermal DNA amplification technique called Recombinase Polymerase Amplification (RPA) in 30 minutes directly from human blood samples. We were able to perform endpoint quantitative digital RPA with a dynamic range of 10∼1000 copies/μl via automatic compartmentalization of the samples. The precise control of fluid flow on chip is accomplished by passive degas-driven flow actuation, which does not require external tubing or pumps, thus making the chip portable. A large amount of sample (∼100μl of blood samples) can be processed. We envision this single-step digital blood plasma separation platform will benefit low cost quantitative molecular diagnostics in both developed and developing countries.

Performance of a hybrid pyroelectric LiNbO3 and TiO2 nanotubes X-ray source

Effects of crystal length and temperature on performance and degradation properties of LiNbO3∕TiO2 pyroelectric∕nanotube X-ray source were studied. Such hybrid LiNbO3∕TiO2 X-ray source was fabricated by bonding electrochemically grown TiO2 nanotubes on -z face of pyroelectric LiNbO3 crystal. In particular, it was found that maximum accelerated electron energy increased with height for both pure and hybrid LiNbO3∕TiO2 system for both heating and cooling cycles. For example, for 2 cm long hybrid structure the resulting maximum energy during heating cycle was 97 keV as compared to 74 keV for 1 cm long structure. The maximum energy for the pure sample without nanotubes increased from 45 keV to 66 keV. Increased endpoint energy of nanotube based X-ray source is attributed to electric field amplification on nanotube tips increasing the efficiency of residual gas ionization, leading to improved charge carrier transmission efficiency. The degradation properties were studied by performing multiple thermal cycles and results revealed that cluster nanotips erode over time. After 20 cycles they become flat as was evidenced from scanning electron microscope analysis.

Thermal modeling and design analysis of a continuous flow microfluidic chip

Although microfluidics has demonstrated the ability to scale down and automate many laboratory protocols, a fundamental understanding of the underlying device physics is ultimately critical to design robust devices that can be transitioned from the benchtop to commercial products. For example, the miniaturization of many laboratory protocols such as cell culture and thermocycling requires precise thermal management. As device complexity scales up to include integrated electrical components, including heating elements, thermal chip modeling becomes an increasingly important part of the design process. In this paper, a computationally efficient, three-dimensional thermal fluidic modeling approach is presented to study the heat transport characteristics of a continuous flow microfluidic thermocycler for polymerase chain reaction (PCR). A two-step simulation model is developed, consisting of a solid domain modeling of the entire microfluidic chip that examines thermal crosstalk due to lateral diffusion across multiple thermal cycles, and a one pass simulation model to study the thermal profile in the fluidic domain as a function of critical parameters like flow rate and microchannel material. The results of the solid domain model are compared against experimental measurements of the thermal profile in a PDMS-glass microfluidic thermocycler device using a combination of thermocouples and an infrared (IR) camera. The suitability of the device in meeting the ideal thermocycling profile at low flow rates is established and it is further shown that higher flow rates lead to deterioration in thermocycling performance. Thermofluidic modeling tools have the potential to streamline the physical microfluidic device design process, reducing the time required to fabricate functional prototypes while maximizing reliability and robustness.

Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n=20). Reproducibility of area counts at two levels, namely 100ppmv and 1000ppmv over a period of two days were found to be less than 5.5% (n=20). Oxygen and nitrogen were found to be linear over a range from 20ppmv to 10,000ppmv with correlation coefficients of at least 0.998 and detection limits of less than 10ppmv. Hydrocarbons of interest were found to be linear over a range from 200ppbv to 1000ppmv with correlation coefficients of greater than 0.999 and detection limits of less than 100ppbv.

Effect of Thermal Loading on ${\rm Nb}_{3}{\rm Sn}$ CICC Performance

The ITER CICC will undergo a number of cool-down and warm-up cycles over the lifetime of the plant. The standard SULTAN based ITER conductor qualification test normally includes one thermal cycle in the test sequence. In many samples a performance degradation was observed following this thermal loading. In order to investigate the effect of multiple thermal cycles on the TF conductor short sample, additional repeated thermal cycles to liquid nitrogen temperature were carried out on the left leg of the CNTF3 sample and the JATF5 sample. Thermal cycles using SULTAN are very time consuming, about four days, with a corresponding cost of around 32 kEuro. Ten thermal cycles will give an estimation of the degradation upon repeated thermal loading, but would require a prohibitive amount of time in SULTAN, and therefore cause a significant delay in the testing of other time critical samples. As a large fraction of the change in thermal contraction occurs between room temperature and liquid nitrogen temperature, a purpose made facility and program was developed. This ad-hoc facility allowed faster, more cost effective thermal cycles that crucially did not interfere with SULTAN's ongoing test program. Cooling and heating was provided by means of forced flow nitrogen. The sample was contained within a vacuum to pre- vent the formation of moisture or ice. During warm-up, a heater distributed around the CNTF3A was also used. These cycles were performed both before and after electromagnetic loading. The results of these tests indicated that thermal loading before the first electromagnetic load cycle did not result in a worsening of the conductor performance. The tests following repeated thermal cycling after electromagnetic loading show a thermal cycle causes a performance degradation but a large number of consecutive thermal cycles do not appear to have a significant effect.

Dislocation Reduction by Glide in Epitaxial IV–VI Layers on Si Substrates

It is explained with a simple model why the reduction of threading dislocation (TD) densities in epitaxial lattice and thermal expansion mismatched IV–VI layers such as PbSe(111) on Si(111) substrates follows a 1/h 2 dependence where h is the thickness of the layer. This is in contrast to the 1/h dependence for III–V and II–VI layers grown on mismatched substrates. The 1/h 2 dependence results since the thermal mismatch strain is mainly reduced by glide and reactions of the TD in their main {100}-type glide system of the NaCl-type IV–VI semiconductors. In addition, multiple thermal cycles lead to further reduction of the TD densities by glide and fusion since fusion does not cause dislocation blocking.

Origin of Microstructural Irreversibility in Ni-Ti Based Shape Memory Alloys during Thermal Cycling

Different microstructures of Ni-Ti- and Ni-Ti-Fe-based shape memory alloys were subjected to thermal cycling: dipping in liquid nitrogen, for approximately 5 minutes, and then bringing it back to room temperature or austenite (cubic: B2) ↔ martensite (monoclinic: B19′) reversible solid-state phase transformation. Direct electron backscattered diffraction (EBSD) observations could bring out aspects of microstructural irreversibilities: namely, changes in grain size, misorientation buildup, and presence of retained martensite. The average changes in grain size (Δd) differed by almost 2 to 4 times between different microstructures. The highest Δd was typically observed in structures having maximum clustering of fine (d < 5 μm) grains. The sample with highest Δd was also subjected to multiple thermal cycling. Although Δd scaled linearly with d after the first thermal cycle, the scatter increased during subsequent thermal cycles. Grain or orientations deviating from the linear behavior were clearly anisotropic crystallographically. With repeated thermal cycling, the patterns of changes in Δd, austenite misorientation, and retained martensite content were similar. A phenomenological model or hypothesis, based on 40 deg \( \left\langle {001} \right\rangle \) orientation relationship between austenite and martensite phases, was proposed to address the observed patterns of microstructural irreversibility.

Analysis of Ti–Ni–Hf shape memory alloys by combinatorial nanocalorimetry

The martensitic transformation in Ti–Ni–Hf thin films with ultra-fine grain structure has been analyzed as a function of composition using a high-throughput array of nanocalorimeters. The martensite–austenite transformation temperature is significantly lower than in bulk Ti–Ni–Hf, but increases linearly with Hf content at a rate comparable to bulk Ti–Ni–Hf. The response to high-temperature cycling (22°C<T<850°C) changes with Ni concentration. For Ni⩽47 at.%, the transformation temperature increases during high-temperature cycling because precipitation of (Ti1−x, Hfx)2Ni enriches the surrounding matrix in Hf; for Ni⩾47.7 at.%, precipitation of the same phase gradually suppresses the transformation. Low-temperature cycling (22°C<T<450°C) causes the transformation temperature to initially decrease and then stabilize. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films is improved compared to previous studies on bulk Ti–Ni–Hf. This is attributed to the very small grain size (18±5nm) of the samples. Alloys with superior thermal cycling stability are identified and the ability to control the transformation temperature through multiple thermal cycling is demonstrated.

Analytical Modeling of Cyclic Thermal Stress and Strain in Plated-Through-Vias With Defects

A previously published analytical model for thermal stress and strain in idealized plated-through-vias (PTVs) has been adapted to conduct elastic-plastic analyses of vias with geometric defects using elastic stress concentration factors calculated earlier. The von Mises stress amplitude, at the mid-plane of the perfect via and at the defect (Δσ0 and Δσ, respectively), and the cumulative plastic von Mises strain, also at the mid-plane of a perfect via and at a defect (e0pl and epl, respectively), compared well with results of finite element analyses (FEAs). Four types of PTV defects were evaluated: barrel thickness reduction, occasional waviness, continuous waviness, and wicking. This model provides a relatively simple alternative to FEA to calculate stresses and strains in vias with defects as well as in perfect vias subjected to multiple thermal cycles. This model provides a tool to investigate quickly the influence of possible PTV design dimensions and defects under thermal cycling conditions (i.e., which are particularly damaging in a given situation). It is much easier than FEA for parametric studies like this. It also provides a means for calculating damage metrics, such as the cumulative von Mises strain, which can then be empirically correlated with the cycles to failure data from thermal cycling tests of PTVs.

Ultra-Low Mass Planar SOFC Design

This work describes Corning Incorporated's early stage efforts to develop an ultra-low mass SOFC design based on a "frit-frame." In this approach, patterned glass or glass-ceramic frit layers perform sealing, manifolding and framing functions without the aid of conventional supporting framing components. In this construction, thermal expansion matching is simplified and thermal mass mismatches are minimized. Consequently planar frit-frame structures can be thermally cycled at comparatively fast rates for SOFC. We show that 12 cm x 15 cm multi-cell packets survive multiple thermal cycles with heating to operating temperature in ten-minutes.

Numerical and experimental investigation of cooling time in laser micro-adjustment of two-bridge actuators

Multiple thermal cycles are necessary in laser micro-adjustment to achieve required deformations. Between two consecutive thermal cycles, a cooling time is necessary for the workpiece to cool down. This paper presents two cooling criteria including the same temperature (ST) and the room temperature (RT) for laser micro-adjustment of two-bridge actuators. The effects of the scaled geometry of actuators on cooling time are investigated numerically and experimentally for different processing parameters under the present cooling criteria. Considering the influence of material properties on cooling time, numerical analysis is conducted for stainless steel and aluminum alloy materials. The effects of the cut-out shapes of actuators are studied using experimental methods. The numerical and experimental results show that the cooling time can be saved significantly when using ST cooling criterion, especially for the material with high thermal conductivity and large heat capacity. Moreover, it was found that the square cut-out actuator be the best choice for different scales if RT is applied. However, for large scales the circle cut-out actuator was found better if ST is used.

Hot Cracking in AZ31 and AZ61 Magnesium Alloy

This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS) was used for component analysis. Results showed that AI content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in AI content, causing higher liquid Mg-alloy rich AI content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone (PMZ). In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher (6 wt%) AI content and produced much liquefied Mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied Mg17Al12 were pulled apart and hot cracks formed at weld metal HAZ due to the augmented strain. Since AZ31 had half the AI content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length (TCL) in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of AI during the welding process, which resulted in lower overall AI content. Consequently, shorter hot cracks exhibited in three thermal cycles. It was found the AI content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.

高クロム鋳鉄のアブレージョン抵抗に及ぼす溶着金属組織の影響

Three commercially available welding consumables were surface welded to mild steel plate. Typical microstructures of their deposited metals were, hypoeutectic (Consumable A), hypereutectic (Consumable B), and hypereutectic with MC type carbides (Consumable C), respectively. The welding parameters were chosen so that the chemical composition of the deposited metals were kept about the same. When the welding was carried out in longitudinal direction with a bead-pitch of 8 mm, the deposited metal cooled rapidly. In contrast, when the welding was carried out reciprocating welding bead in transverse direction with a small bead-pitch of 3 mm, thermal cycle became shorter and the temperature of the welding zone was raised by the effect of multiple thermal cycles, resulting in a slow cooling of the deposited metals. Besides the thermal cycles, the thickness of the base plate was changed from 25 to 12 mm to reduce the cooling rate of the deposited metal. Abrasion resistance of each deposited metal was evaluated by the rubber wheel test. Main results obtained were as follows;(1) By the preheating effect of multiple thermal cycles, the cracking of the high Cr cast-iron deposited metals was reduced remarkably.(2) In general, the wear loss of the deposited metal was decreased as the hardness increased.(3) The wear loss of the consumable A deposited metal was decreased when cooled slowly and larger austenitic dendrite and inter-dendritic eutectic carbides were formed.(4) The wear loss of the consumable B deposited metal was decreased when cooled rapidly and primary carbides were surrounded by austenitic eutectic matrixes.(5) The consumable C deposited metals, in which MC type carbides and primary-like carbides were dispersed in austenitic matrixes, showed the best abrasion resistance among the consumables investigated.

Thermal effects in Ge‐Sb‐Te phase‐ change memory materials during multiple thermal cycling

AbstractPhase transformations in (GeTe)m(Sb2Te3)n (m: n = 1:1; 1:2; 2:1) alloys and thin films on their basis were studied during thermal cycling by differential scanning calorimetry, and some thermal properties were determined. Exothermal peaks due to the amorphous → crystalline phase changes were observed in all thin films. In addition, reproducible endothermic peak in the range of 390‐415 °C was revealed in thin films as well as in bulk Ge2Sb2Te5, GeSb2Te4, GeSb4Te7 samples, which may influence on the kinetics and endurance of data reading processes in phase‐change memory devices. Activation energies of observed heat effects were estimated with using Kissinger's method, and nature of the given endothermic peak was discussed. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study of martensitic transformation in the Fe-22 Mn-3 Si alloy by mechanical spectroscopy

Methods of mechanical spectroscopy (determination of the internal-energy dissipation and the elasticity modulus), X-Ray diffraction, and calorimetry have been used to study the specific features of the reversible martensitic transformation in the Fe—22Mn—3Si alloy (wt %). A detailed study has been given to the specific features of the internal-energy dissipatio n during the direct and reverse martensitic transformations in a wide range of heating rates, frequencies, and deformation amplitudes. Particular emphasis has been placed on multiple thermal cycling of the sample through the martensitic-transformation range and its effect on the martensitic-transformation parameters, such as the transformation start and finish temperatures, the value of the thermal hysteresis, and the transformation kinetics.

Delayed Hydride Cracking Initiation at Notches in Zr-2.5Nb Alloys

Delayed hydride cracking (DHC) is an important crack initiation and growth mechanism in Zr-2.5Nb alloy pressure tubes of CANDU nuclear reactors. DHC is a repetitive process that involves hydrogen diffusion, hydride precipitation, growth, and fracture of a hydrided region at a flaw tip. In-service flaw evaluation requires analyses to demonstrate that DHC will not initiate from the flaw. The work presented in this paper examines DHC initiation behavior from V-notches with root radii of 15 μm, 30 μm, and 100 μm, which simulate service-induced debris fretting flaws. Groups of notched cantilever beam specimens were prepared from two unirradiated pressure tubes hydrided to a nominal hydrogen concentration of 57 wt. ppm. The specimens were loaded to different stress levels that straddled the threshold value predicted by an engineering process-zone (EPZ) model, and subjected to multiple thermal cycles representative of reactor operating conditions to form hydrides at the notch tip. Threshold conditions for DHC initiation were established for the notch geometries and thermal cycling conditions used in this program. Test results indicate that the resistance to DHC initiation is dependent on notch root radius, which is shown by optical metallography and scanning electron microscopy to have a significant effect on the distribution and morphology of the notch-tip reoriented hydrides. In addition, it is observed that one tube is less resistant to DHC initiation than the other tube, which may be attributed to the differences in their microstructure and texture. There is a reasonable agreement between the test results and the predictions from the EPZ model.

Stability of electrical switching properties in vanadium dioxide thin films under multiple thermal cycles across the phase transition boundary

The influence of successive thermally induced metal-insulator transition (MIT) on electrical transition characteristics in high quality vanadium dioxide (VO2) thin films synthesized by reactive sputtering was investigated in conjunction with structural studies. We show that the transition quality of VO2 thin films was largely unaffected up to ∼100 heating-cooling cycles with respect to hysteresis width, resistivity ratio, and MIT onset temperature. The hysteresis width decreased by ∼3% along with an enhancement in film texture, while no reduction in resistivity ratio or MIT temperature was observed, implying that the stoichiometry of overall VO2 thin film did not degrade under multiple thermally induced transitions. The results are of potential relevance to solid state sensing elements utilizing vanadium oxide.

Characterisation of a silicon photomultiplier device for applications in liquid argon based neutrino physics and dark matter searches

The performance of a silicon photomultiplier has been assessed at low temperature in order to evaluate its suitability as a scintillation readout device in liquid argon particle physics detectors. The gain, measured as 2.1 × 106 for a constant over-voltage of 4V was measured between 25°C and -196°C and found to be invariant with temperature, the corresponding single photoelectron dark count rate reducing from 1MHz to 40Hz respectively. Following multiple thermal cycles no deterioration in the device performance was observed. The photon detection efficiency (PDE) was assessed as a function of photon wavelength and temperature. For an over-voltage of 4V, the PDE, found again to be invariant with temperature, was measured as 25% for 460nm photons and 11% for 680nm photons. Device saturation due to high photon flux rate, observed both at room temperature and -196°C, was again found to be independent of temperature. Although the output signal remained proportional to the input signal so long as the saturation limit was not exceeded, the photoelectron pulse resolution and decay time increased slightly at −196°C.

Tribological coatings for lubrication over multiple thermal cycles

Nanocomposite materials demonstrating multiple temperature-adaptive mechanisms including diffusion, oxidation and/or catalysis mechanisms to yield low friction coefficients of < 0.2 from room temperature to 700 °C were combined with diffusion barrier layers in coatings with different architectures (e.g., layer thicknesses, number of layers, etc.) to examine adaptation of contact surface chemistry and morphology over multiple thermal cycles. Multilayered coatings consisting of ceramic–metal nanocomposite adaptive lubricant layers separated by diffusion barriers allowed adaptation to occur only upon exposure of the lubricant layer by wear, which resulted in prolonged wear life at static and cycled temperatures. It was also observed that a relationship between the number of adaptive lubricant layers and the number of thermal cycles existed, where one thermal cycle consumed two adaptive lubricant layers. The thickness of the adaptive coating layers was also important because diffusion- and oxidation-based adaptation in these particular coatings required a minimum volume of solid lubricant material. The surface roughness of the adaptive coating materials played a significant role in their performance within multilayered coatings, where rough coatings (> 100 nm R a) failed after relatively few sliding cycles. The utility and application of adaptive coatings materials providing lubrication over multiple thermal cycles is discussed.

Deposition of Ti–6Al–4V using a high power diode laser and wire, Part II: Investigation on the mechanical properties

The deposition with high power diode laser and Ti6Al4V wire was verified as a process which can provide a high deposition rate with good quality. Sound mechanical properties of the deposited parts are the prerequisites for the real applications of this process. In this paper, the main mechanical properties including micro-hardness and tensile properties were investigated. Single bead walls were deposited. Test pieces were machined from the deposited walls according to the British standard for the mechanical tests. The epitaxial columnar grains were found growing parallel to the building direction. A band region was observed between two deposited layers, which resulted from the remelting of previously deposited layer and multiple thermal cycles that had occurred with each subsequent deposition pass. The results showed that with the same laser power, the built samples with higher traverse speed possess similar or slightly higher hardness than the samples built with lower traverse speed. The hardness varied less than 10% with different sets of parameters. The investigations on the tensile properties were carried out with the samples as deposited and stress relieved at 700 °C in an air circulating furnace for 2 h. The as deposited samples showed better tensile properties than the stress relieved ones. This results from the reduction of the compressive residual stresses and the coarser microstructure after stress relief. The tensile properties also showed dependence on the direction of the test carried out. All the examined tensile properties of the as deposited samples matched properties of the as cast and wrought material.