Ultra-low Level Research Articles

Process Control for Advanced Packaging Metallization

Despite advances in optical interconnect, metal interconnect remains the dominant technology, however the type and diversity of metal structures is rapidly changing. Wire-bonding cannot meet required interconnect density and is being replaced with electrodeposition-based flip chip technology. Modern packaging scheme required high diversity of interconnects within the same device: RDL, mircobump, pillar, TSV, tall (mega) pillar, etc. using sequential deposition of different metals such as Cu, Ni, SnAg/Sn, Au. Diverse challenging requirement leads to evolution of chemistries and process control approaches. Many 20th century chemistries were limited to 1 organic additive for Cu process. Today, up to 4 individual additives are used to dial the process. While most of semiconductor front end processing enjoys the luxury of single-use chemistry, it is not yet considered a viable option for electrodeposition. The same electrolyte can be used for processing over 1000 parts in replenishment mode. Maintaining performance under these conditions requires close monitoring of component breakdown and contaminants accumulated in the processes. There is also a real possibility for disproportional trends for individual components of replenishment package. It is no longer enough to monitor just main 3–6 components of the bath. Successful high volume metallization for advanced packaging requires comprehensive metrology/process control. Presentation will provide specific examples of metrology and process control strategy for various metallization solution with emphasize on breakdown products and contaminants. There is no single technology which can cover diversity of metrology needs. CVS is a versatile technology which can be used not only for control of main additives but also to monitor breakdown products of accelerator, suppressor, leveler, Cu(I) contaminants, H2O2 contaminant and even leached photoresist. In case of Ni chemistry, it is useful to monitor breakdown products of sulfamate. UV-Vis spectroscopy shines at monitoring of leached photoresists, Fe(III), breakdown products of sulfamate as well as control of many main components: Cu, Ni, Co, Au, additives. ICP is the best for ultra low level of metal contaminants which can harms deposition process, as well as low level of some target components, like Tl in Au. Novel approach is developed to track additive turnover process based on ICP results. HPLC is valuable to characterize multiple breakdown products of organic additives, while ion chromatography helps to track transformation of ions, such as oxidation of sulfite to sulfate in Au solution. Surface tension aids monitoring of surfactants and their degradation. It is important to differentiate between R&D study and robust “fit-to-purpose” practical process control. While Ion Chromatography approach would be more appropriate for academic study and perhaps process development, simple robust methods like titration, specific gravity are preferable for industrial process control. Similarly, HPLC is a great scientific tool but CVS, spectroscopy and titration are better fit and safer alternative for in-fab operation. Presentation will provide specific examples and comparative analysis of different analytical methods.

Toward a Label-Free Electrochemical Impedance Immunosensor Design for Quantifying Cortisol in Tears.

Cortisol is a viable biomarker for monitoring physiological, occupational, and emotional stress and is normally present in tear fluid at approximately 40 nM, or higher as a result of stress. We present characterization and quantification of cortisol via several electrochemical methods versus the standard enzyme-linked immunosorbent assay, commonly known as ELISA. We also present a prototyped design of a disposable test strip and handheld sensor based on label-free electrochemical impedance spectroscopy to quantify cortisol levels in tear fluid within approximately 90 seconds. Electrochemical characterization of the cortisol molecule was conducted using cyclic voltammetry, amperometric i-t, and square wave voltammetry. Lower limits of detection for these techniques were not sufficient to quantify cortisol and phycological tear ranges: 0.1 M, 0.23 M, and 193 M for cyclic voltammetry, amperometric i-t, and square wave voltammetry, respectively. However, electrochemical impedance spectroscopy (EIS) was to be the best mode of cortisol quantification and comparison to ELISA technique (detection range of ~ 138 pM - 552 nM). The initial EIS biosensor obtained a lower limit of detection of 59.76 nM with an approximate 10% relative standard deviation. The cortisol assay and tear collection prototype presented here offer a highly reproducible and ultra-low level of detection with a label-free and rapid response.

Ultra-Low Level Light Detection Based on the Poisson Statistics Algorithm and a Double Time Windows Technique With Silicon Photomultiplier

In this paper, we present a method to detect ultra-low level light ranging from several mean photoelectrons (MPEs) down to 10−5 MPEs. It is based on the Poisson statistics algorithm and a double time windows technique with a silicon photomultiplier (SiPM) and a field programmable gate array (FPGA). It measures the mean incident photoelectron number of pulsed light with zero peak statistics of the Poisson distribution to reduce the influence of the correlation noises and the dark count rate (DCR) fluctuation. The linear measurement ranges from ~10−4 MPEs to ~10 MPEs (i.e., ~97 dB) were demonstrated with double 35-ns time windows at room temperature. Its upper detection limit is determined by the availability for the zero peak counts of the Poisson distribution, and the lower detection limit is mainly determined by the DCR of the SiPM. By narrowing the time window to ~550 ps or decreasing the operating temperature of SiPM to −30 °C, the detection limit can be further decreased to ~10−5 MPEs. This method, with capability to record the arrival time of incident photons, demonstrated an instrument response function (IRF) of ~214.9 ps (FWHM), showing its compatibility to the time correlated photon counting (TCPC) technique and the time of flight (TOF) measurement.

Imitational modeling of synchronous measuring detector with increased noise immunity and precision

In this paper, an example of application, simulation results, noise and precision properties of a synchronous measuring detector with increased noise immunity and precision (not less than 1%) for the operation providing of primary sensors – thermal sensors and bridge sensors, in particular Hall sensors for magnetic field measurements are considered. As a result of the research, it was discovered that increasing the sensitivity of magnetometers based on Hall sensors leads to the allocation of the initial useful signal of the ultra-low level against the background of noise comparable with it. To allocate the output signal of the Hall sensor or thermal sensor in the background of noise, it is proposed to feed it with harmonic current with the further allocation of the information signal using a in-phase detector with a narrowband low-pass filter.

Effect of hydrogen peroxide additive on the combustion and emission characteristics of an n-butanol homogeneous charge compression ignition engine

The homogeneous charge compression ignition (HCCI) combustion was conducted on a modified engine to investigate the effect of hydrogen peroxide (H2O2) additive on the combustion and emission characteristics, such as the indicated thermal efficiency (ηi), the total hydrocarbon (THC), the carbon monoxide (CO) and the nitrogen oxides (NOx) emissions. A simulation using CHEMKIN software was also performed to analyze the experimental data. The results indicate that the addition of H2O2 facilitates the formation of hydroxyl (OH) radical and hydroperoxyl (HO2) radical in the cylinder under HCCI mode, which greatly affects the combustion and emission characteristics of the n-butanol HCCI engine. By adding H2O2, ηi increases, NOx emission remains at an ultra-low level, but THC and CO emissions reduce at almost all the test conditions. Especially at the low intake temperature (Tin) or low load condition, the improvements are very obvious, which suggests that addition of H2O2 may extend the low Tin and low load limits of HCCI engines.

Direct injection mass spectrometry technique for the odorant losses at ppb(v) level from nalophan™ sampling bags

Trace compound stability is crucial for real time gas analysis and for high efficiency energy generators, where part per billion concentrations have a high impact. In this context, the container type chosen for the gas analysis becomes important. Several types of containers, such as stainless-steel canisters, glass bulbs, gas tight syringes and sampling bags can be adopted for sampling and storing such samples. Sampling bags are cheap and easy to manage, for these reasons other solutions are rarely used. Literature studies have showed how nalophan™ bags represent the best choice for the collection of samples due to the extremely low cost, the good sample stability and the low background interaction. No studies have considered the biogas trace constituents, especially at an ultra-low concentration level. Most of the studies relating to trace compound detection, use a GC–MS instrument and focus on few compounds of interest. In this paper, one of the most rapid and reliable direct injection mass spectrometry techniques was used. PTR-QMS was adopted to investigate the real biogas mixture stability. The concentration losses were studied continuously during 24 h from the sampling. These losses may be related to the wall adsorption and/or through the wall diffusion phenomena. The most stable compounds detected were acetone, methanol and formaldehyde with a concentration loss below 5%. Terpenes and sulphur compounds had a concentration loss of around 50%, while hydrocarbons and aromatic compounds showed concentration losses around 60%. The stability of the compounds monitored with acceptable losses (below 5%), was achieved within the first 3 h after the sampling was carried out.

The Camels in Balochistan: Status, farming practices and camel centered measures

Abstract This study is based on primary and secondary data encompassing status of camels and camel farmers, prevailing farming practices and camel centered measures in Balochistan, Pakistan. The key purpose is to give a glimpse to the policy makers about this neglected species that is bestowed with unearthed potentials. The province Balochistan has the lion’s share (41%) of total camel population of Pakistan. The documented breeds in this region are seven out of total twenty breeds in Pakistan. The study explains that the camel famers are illiterate and living ultra low level life standards. The camel farming is on traditional pattern. Grazing has poor nutritive value resulting in delayed growth, puberty age, conception rate, increased calving interval and low milk yield. Milk marketing is not favored coupled with lack of market knowledge for selling live camels. The academic and administrative focus on camel’s research and development is rare at all levels. It is high time to work on camel, camel farmer and camel farming with multi-pronged strategy. Educating camel farmers in field schools and adoption of scientific farming procedures, milk and meat marketing, value addition of milk and dairy products are the ways to move forward. Keywords: Balochistan; Camel; Farming; Poverty; Trends http://dx.doi.org/10.19045/bspab.2018.700209

Investigation of fast screening LSC method for monitoring 14C activity in wastewater samples

This paper explores the possibility of a direct measurement of 14C activity concentration in wastewater without chemical pretreatment of samples, which would provide the advantages such as rapidity, low-cost, and simplicity of radioanalysis that is desirable in the case of nuclear emergencies. A method via Liquid Scintillation Counting (LSC) technique has been implemented and optimized. The method assumes mixing of the water sample with a scintillation cocktail (Permafluor E+ and Ultima Gold AB cocktails were tested). Measurements were performed on Ultra Low Level Liquid Scintillation Spectrometer Wallac 1220 Quantulus. Optimization of the method included optimal water:cocktail volume ratio, optimal counting window selection, PAC (Pulse Amplitude Comparator) parameter adjustment, based on the highest FOM (Figure of Merit) value achieved, as well as detection efficiency and detection limit evaluation. The main problem in such an approach, interference with other beta emitters that are often present in wastewater samples, has been discussed. The possibility to eliminate low-energy counts that would be generated from 3H, and to estimate the contribution of other high-energy beta emitters to obtained results of 14C content is presented as well. Method's constraints, its accuracy, and precision have been considered from the obtained results of measurements of wastewater samples. Its application is limited only to 14C screening of samples with much higher 14C activities than those of the environmental (surface and ground) waters. Presented results could be used as guiding principles of development, optimization, and implementation of the fast 14C screening method in other laboratories.

Synthesis of novel MnCo2O4/NaY zeolite nanocomposite adsorbent and its performance for Sr2+ ions removal from drinking water

The present study describes the effective performance of MnCo2O4/NaY zeolite (MnCo2O4: 18.7 wt%) as a novel nanocomposite adsorbent for the removal of Sr2+ ions from drinking water of Tehran city. The reactions were all carried out under pre-organized optimized conditions and the subsequent monitoring was accomplished via the ultra-low level liquid scintillation counting (LSC) analysis. The characterization study of samples was carried out using scanning electron microscope, energy dispersive X-ray, atomic force microscope, powder X-ray diffraction and Fourier-transform infrared spectroscopy. Multiple experimental conditions including adsorbent dose, pH, adsorbent type and contact time were applied for the adsorption-removal process of Sr2+ ions by the MnCo2O4/NaY nanocomposite adsorbent. The results from LSC concluded that Sr2+ was operatively adsorbed on the nanocomposite surface active sites after 180 min at room temperature with a yield more than 95%. The reaction kinetic data was precisely studied by employing pseudo-first and second-orders, intra particle diffusion and Elovich models. The adsorption kinetics was found to fit the pseudo-second-order model. Moreover, the investigation of the thermodynamic parameters such as $$\varDelta {\text{G}}^{0}$$ , $$\varDelta {\text{H}}^{0}$$ and $$\varDelta {\text{S}}^{0}$$ , specified that adsorption procedure of Sr2+ was spontaneous and expresses a physic-chemical adsorption characteristics and exothermic feature of the adsorption reaction. The sequential experiments of reproducibility for the synthesized nanocomposite against Sr2+ ions showed removal efficiency of more than 91% for all those cycles.

Enhanced Oil Recovery Potential of Alkyl Alcohol Polyoxyethylene Ether Sulfonate Surfactants in High-Temperature and High-Salinity Reservoirs

Surfactant flooding has been widely applied in high-temperature and high-salinity reservoirs. In this paper, the enhanced oil recovery potential of alkyl alcohol polyoxyethylene ether sulfonate (CEOS) was investigated in a combined study of surface activity, crude oil–water interfacial tension (IFT) reduction, emulsifying property, wettability improvement, and macroscopic oil displacement efficiency. The results illustrated that CEOS had high surface activity and IFT could be reduced to an ultralow level (10–3 mN/m) at high-temperature and high-salinity conditions. When salinity ranged from 15 × 104 to 22.5 × 104 mg/L and reservoir permeability was ∼10 mD, linear CEOS solution could effectively displace crude oil for its favorable IFT reduction ability. Linear CEOS or CEOS with a benzene ring was optimized for their favorable IFT reduction ability or emulsifying ability when reservoir permeability was ∼50 mD or non-homogeneous. A 0.5 pore volume surfactant flooding and subsequent water flooding could rema...

An experimental study on the mechanisms of enhancing oil recovery by nanoparticles-assisted surfactant flood

ABSTRACT The central concern of this study is to examine the synergic effects of an anionic surfactant and hydrophilic silica nanoparticles on the improvement of surfactant properties. The assessment of the effect of silica nanoparticles on the emulsification ability of the surfactant solution was performed by the use of both electrical conductivity measurements and phase behavior tests. Accordingly, an optimal chemical formulation for the utilized crude oil was suggested. Optical absorption technique was also employed to evaluate the stability of the optimal solution. The oil recovery experiments were carried out in a transparent glass micromodel saturated with crude oil to monitor some pore-scale displacement events during the simultaneous flow of the optimal solution and the crude oil through porous media. Phase behavior tests indicated that the silica nanoparticles are effective in terms of Interfacial tension (IFT) reduction since they can achieve ultra-low IFT level. The results of conductivity experiments proved the ability of silica nanoparticles to reduce the Critical Micelle Concentration (CMC) of the surfactant. The stability tests proved that the optimal solution is stable for a reasonable time. The multiphase flow experiments revealed that oil recovery increased by about 5% during nanoparticles-assisted surfactant flooding compared with surfactant flood.

MICROEMULSION FLOODING MECHANISM FOR OPTIMUM OIL RECOVERY ON CHEMICAL INJECTION

The formation of microemulsion in the injection of surfactant at chemical flooding is crucial for the effectiveness of injection. Microemulsion can be obtained either by mixing the surfactant and oil at the surface or injecting surfactant into the reservoir to form in situ microemulsion. Its translucent homogeneous mixtures of oil and water in the presence of surfactant is believed to displace the remaining oil in the reservoir. Previously, we showed the effect of microemulsion-based surfactant formulation to reduce the interfacial tension (IFT) of oil and water to the ultralow level that suffi cient enough to overcome the capillary pressure in the pore throat and mobilize the residual oil. However, the effectiveness of microemulsion flooding to enhance the oil recovery in the targeted representative core has not been investigated.In this article, the performance of microemulsion-based surfactant formulation to improve the oil recovery in the reservoir condition was investigated in the laboratory scale through the core flooding experiment. Microemulsion-based formulation consist of 2% surfactant A and 0.85% of alkaline sodium carbonate (Na2CO3) were prepared by mixing with synthetic soften brine (SSB) in the presence of various concentration of polymer for improving the mobility control. The viscosity of surfactant-polymer in the presence of alkaline (ASP) and polymer drive that used for chemical injection slug were measured. The tertiary oil recovery experiment was carried out using core flooding apparatus to study the ability of microemulsion-based formulation to recover the oil production. The results showed that polymer at 2200 ppm in the ASP mixtures can generate 12.16 cP solution which is twice higher than the oil viscosity to prevent the fi ngering occurrence. Whereas single polymer drive at 1300 ppm was able to produce 15.15 cP polymer solution due to the absence of alkaline. Core flooding experiment result with design injection of 0.15 PV ASP followed by 1.5 PV polymer showed that the additional oil recovery after waterflood can be obtained as high as 93.41% of remaining oil saturation after waterflood (Sor), or 57.71% of initial oil saturation (Soi). Those results conclude that the microemulsion-based surfactant flooding is the most effective mechanism to achieve the optimum oil recovery in the targeted reservoir.

A novel electrochemical sensor for bisphenol A detection based on nontarget-induced extension of aptamer length and formation of a physical barrier

In this study, a novel electrochemical sensing strategy was developed based on nontarget-induced bridge assembly and aptamer (Apt) extension reaction triggered by terminal deoxynucleotidyl transferase (TdT). Bisphenol A (BPA) was chosen as the target analyte to study the analytical performance of the designed aptasensor. This sensing system takes advantages of electrochemical sensing platforms and detection of an ultra-low level of BPA, due to the formation of bridge on the surface of electrode in the absence of BPA. In the presence of BPA, Apt/BPA complex is formed and inhibits the access of TdT to the 3′-end of Apt, resulting in the lack of bridge assembly and high access of [Fe(CN)6]3-/4- as redox agent to the electrode surface. Thus, a strong redox peak is observed. This aptasensor enabled the selective detection of BPA with the wide linear range of 0.08–15 nM and detection limit as low as 15 pM. Furthermore, the presented sensing platform was successfully applied for the detection of BPA in tap water and grape juice samples.

Mechanistic Modeling of Nanoparticles-Assisted Surfactant Flood

High interfacial tension (IFT) between oil and water brings about high capillarity leading to high residual oil saturation. Surfactants are employed to reduce IFT or modify wettability and mobilize the trapped oil. This paper aims to investigate the interaction of sodium dodecyl sulfate as a surfactant and two types of silica nanoparticles in different particle sizes for the purpose of enhancing oil recovery. Accordingly, the effect of employed nanoparticles on the critical micelle concentration (CMC) of the surfactant was investigated by the use of electrical conductivity measurements. Phase behavior studies were also carried out to examine the solubilizing ability of the surfactant and nanoparticles assembly. Based on the analysis of solubilization curves, an ultra-low IFT chemical formulation for the target reservoir crude oil was identified and the stability of the optimum solutions was examined through visual observation, optical absorption, and zeta potential measurements. The oil recovery experiments were performed in a quarter five-spot transparent pore network model saturated with crude oil to observe the displacement behavior of the injectant and its influence on oil recovery. Phase behavior tests indicated that the silica nanoparticles smaller in size are more effective in terms of IFT reduction since they can achieve ultra-low IFT level, and the conductivity measurements showed they relatively reduce the CMC of the surfactant. The results of stability tests demonstrated the optimum solutions are stable for more than 1 week. The micromodel experiments displayed that oil recovery increased by 4% during nanoparticles-assisted surfactant flood in comparison with surfactant flood.

The ultra-low interfacial tension behavior of the combined cationic/anionic-nonionic gemini surfactants system for chemical flooding

Gemini surfactants have attracted intensive attention owning to their unique physical and chemical properties and have gradually been applied in the field of enhanced oil recovery (EOR). In this work, a combined cationic/anionic-nonionic gemini surfactant system consisting of cetyltrimethyl ammonium bromide (CTAB) and anionic-nonionic gemini surfactants (GAES-9) was proposed for EOR. The surface performance of the combined system was superior to that of either surfactant alone. Critical micelle concentration (CMC) data were used to calculate the molecular interaction parameters according to the regular solution theory. The combined CTAB/GAES-9 surfactant system could greatly affect the interfacial tension (IFT) between water and crude oil, and the strength of this effect depended on the mole fraction and concentration of CTAB/GAES-9. The system could reduce the IFT to an ultra-low level at a total concentration of 200 mg/L, and the system could still maintain ultra-low IFT at a salinity of 10 × 104 mg/L. The mechanism underlying the synergistic effect of CTAB/GAES-9 to obtain ultra-low IFT was systematically investigated. It is most probably related to a large number of anions and cations being adsorbed onto the oil-water interface due to electrostatic attraction. Meanwhile, the spatial structure of the elongated, flexible EO chains in the gemini surfactant entangled at the oil-water interface shields some CTAB cations, enabling the adsorption of more cations. To summarize, the combined surfactants exhibit remarkable abilities and could serve as a candidate for EOR in harsh reservoirs.

Adoption of phase behavior tests and negative salinity gradient concept to optimize Daqing oilfield alkaline-surfactant-polymer flooding

A high performance surfactant formulation was developed using more universally accepted Winsor type phase behavior tests rather than relying primarily on interfacial tension (IFT) measurement for the first time for Daqing oilfield. A surfactant mixture of alkylbenzene sulfonate and fatty alcohol propoxylated ether sulfate was identified which was able to form middle-phase microemulsion with Daqing less reactive crude oil (acid number below 0.1 mg KOH/g crude), lower oil water IFT to ultralow level, and hold desired aqueous stability. Winsor type phase behavior tests at various water oil ratios (WORs) showed the optimum salinity changed slightly from 1.95% to 2% when WOR was increased from 5:5 to 9:1 due to the low reactivity of the Daqing crude oil. To investigate the significance of salinity on Daqing alkaline-surfactant-polymer (ASP) flooding, 4 salinity profiles were designed during coreflooding that corresponded to different types of microemulsions including III–III–I, I–III–I, II–III–I, and III–III–III. For each coreflooding, 0.3 pore volume (PV) of ASP slug with 0.3% total surfactant concentration and 0.2 PV polymer drive was injected. The results demonstrated when negative salinity gradient (3.0%–2.0%–0.5% Na2CO3 in waterflood, ASP, and polymer slugs) was applied, the highest incremental oil recovery of 45.9% original oil in place (OOIP) was achieved. If no Na2CO3 was added in water preflush prior to the injection of ASP slug, the lowest incremental recovery of 32.8% OOIP was observed. For a constant salinity profile at optimum salinity, an intermediate oil recovery (37.4%) was encountered. The measurement of surfactant and Na2CO3 concentrations in the effluents indicated that when negative salinity gradient (II–III–I) was applied, the surfactant loss in the porous media and the oil phase was moderate compared to the two corefloods with III–III–III (highest surfactant loss) emulsion and I–III–I emulsion (lowest surfactant loss). This implied that at optimized salinity profile, the surfactants were more close to hydrophobic-hydrophilic balance during the propagation in the reservoir, which showed the highest potential of increasing oil recovery for the Daqing Oilfield without significantly increasing chemical consumption.

Determination of ultra-low level plutonium isotopes (239Pu, 240Pu) in environmental samples with high uranium

In order to measure trace plutonium and its isotopes ratio (240Pu/239Pu) in environmental samples with a high uranium, an analytical method was developed using radiochemical separation for separation of plutonium from matrix and interfering elements including most of uranium and ICP-MS for measurement of plutonium isotopes. A novel measurement method was established for extensively removing the isobaric interference from uranium (238U1H and 238UH2+) and tailing of 238U, but significantly improving the measurement sensitivity of plutonium isotopes by employing NH3/He as collision/reaction cell gases and MS/MS system in the triple quadrupole ICP-MS instrument. The results show that removal efficiency of uranium interference was improved by more than 15 times, and the sensitivity of plutonium isotopes was increased by a factor of more than 3 compared to the conventional ICP-MS. The mechanism on the effective suppress of 238U interference for 239Pu measurement using NH3-He reaction gases was explored to be the formation of UNH+ and UNH2+ in the reactions of UH+ and U+ with NH3, while no reaction between NH3 and Pu+. The detection limits of this method were estimated to be 0.55 fg mL-1 for 239Pu, 0.09 fg mL−1 for 240Pu. The analytical precision and accuracy of the method for Pu isotopes concentration and 240Pu/239Pu atomic ratio were evaluated by analysis of sediment reference materials (IAEA-385 and IAEA-412) with different levels of plutonium and uranium. The developed method were successfully applied to determine 239Pu and 240Pu concentrations and 240Pu/239Pu atomic ratios in soil samples collected in coastal areas of eastern China.

Viscoelastic Surfactants with High Salt Tolerance, Fast‐Dissolving Property, and Ultralow Interfacial Tension for Chemical Flooding in Offshore Oilfields

AbstractInjected chemical flooding systems with high salinity tolerance and fast‐dissolving performance are specially required for enhancing oil recovery in offshore oilfields. In this work, a new type of viscoelastic‐surfactant (VES) solution, which meets these criteria, was prepared by simply mixing the zwitterionic surfactant N‐hexadecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (HDPS) or N‐octyldecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (ODPS) with anionic surfactants such as sodium dodecyl sulfate (SDS). Various properties of the surfactant system, including viscoelasticity, dissolution properties, reduction of oil/water interfacial tension (IFT), and oil‐displacement efficiency of the mixed surfactant system, have been studied systematically. A rheology study proves that at high salinity, 0.73 wt.% HDPS/SDS‐ and 0.39 wt.% ODPS/SDS‐mixed surfactant systems formed worm‐like micelles with viscosity reaching 42.3 and 23.8 mPa s at a shear rate of 6 s−1, respectively. Additionally, the HDPS/SDS and ODPS/SDS surfactant mixtures also exhibit a fast‐dissolving property (dissolution time <25 min) in brine. More importantly, those surfactant mixtures can significantly reduce the IFT of oil–water interfaces. As an example, the minimum of dynamic‐IFT (IFTmin) could reach 1.17 × 10−2 mN m−1 between the Bohai Oilfield crude oil and 0.39 wt.% ODPS/SDS solution. Another interesting finding is that polyelectrolytes such as sodium of polyepoxysuccinic acid can be used as a regulator for adjusting IFTmin to an ultralow level (<10−2 mN m−1). Taking advantage of the mobility control and reducing the oil/water IFT of those surfactant mixtures, the VES flooding demonstrates excellent oil‐displacement efficiency, which is close to that of polymer/surfactant flooding or polymer/surfactant/alkali flooding. Our work provides a new type of VES flooding system with excellent performances for chemical flooding in offshore oilfields.

An Area and Energy Efficient Ultra-Low Voltage Level Shifter With Pass Transistor and Reduced-Swing Output Buffer in 65-nm CMOS

This brief presents an ultra-low voltage level shifter (LS) with fast and energy-efficient voltage conversion from the deep subthreshold region to the superthreshold region. The proposed LS achieves better performance and increased energy efficiency by addressing the reduced swing and the slow fall transition issues in prior arts. A novel reduced-swing buffer design is proposed to attain lower standby power consumption while a pass transistor is used for improving the speed of the fall transition. The proposed LS consists of only 11 transistors occupying $7.45~ {\mu }\text{m}^{2}$ , which obtains the smallest area among the state-of-the-art ultra-low voltage LSs. Measurement results from a test chip fabricated in 65-nm CMOS technology demonstrate that the proposed LS shows the maximum leakage and speed improvements of $16.3{\times}$ and $2.7{\times}$ compared to the Wilson current mirror LS. The proposed LS also accomplishes the maximum switching energy reduction of $8.5{\times}$ and can convert deep subthreshold voltage as low as 100 mV to the superthreshold voltage of 1.2 V.

A photon recycling approach to the denoising of ultra-low dose X-ray sequences.

Clinical procedures that make use of fluoroscopy may expose patients as well as the clinical staff (throughout their career) to non-negligible doses of radiation. The potential consequences of such exposures fall under two categories, namely stochastic (mostly cancer) and deterministic risks (skin injury). According to the "as low as reasonably achievable" principle, the radiation dose can be lowered only if the necessary image quality can be maintained. Our work improves upon the existing patch-based denoising algorithms by utilizing a more sophisticated noise model to exploit non-local self-similarity better and this in turn improves the performance of low-rank approximation. The novelty of the proposed approach lies in its properly designed and parameterized noise model and the elimination of initial estimates. This reduces the computational cost significantly. The algorithm has been evaluated on 500 clinical images (7 patients, 20 sequences, 3 clinical sites), taken at ultra-low dose levels, i.e. 50% of the standard low dose level, during electrophysiology procedures. An average improvement in the contrast-to-noise ratio (CNR) by a factor of around 3.5 has been found. This is associated with an image quality achieved at around 12 (square of 3.5) times the ultra-low dose level. Qualitative evaluation by X-ray image quality experts suggests that the method produces denoised images that comply with the required image quality criteria. The results are consistent with the number of patches used, and they demonstrate that it is possible to use motion estimation techniques and "recycle" photons from previous frames to improve the image quality of the current frame. Our results are comparable in terms of CNR to Video Block Matching 3D-a state-of-the-art denoising method. But qualitative analysis by experts confirms that the denoised ultra-low dose X-ray images obtained using our method are more realistic with respect to appearance.