• Capture and sorting of multiple cells by polarization-controlled three-beam interference

      Hou, Yu; Wang, Zuobin; Hu, Yaowei; Li, Dayou; Qiu, Renxi; Changchun University of Science and Technology; University of Bedfordshire (IOP PUBLISHING LTD, 2016-02-02)
      For the capture and sorting of multiple cells, a sensitive and highly efficient polarization-controlled three-beam interference set-up has been developed. With the theory of superposition of three beams, simulations on the influence of polarization angle upon the intensity distribution and the laser gradient force change with different polarization angles have been carried out. By controlling the polarization angle of the beams, various intensity distributions and different sizes of dots are obtained. We have experimentally observed multiple optical tweezers and the sorting of cells with different polarization angles, which are in accordance with the theoretical analysis. The experimental results have shown that the polarization angle affects the shapes and feature sizes of the interference patterns and the trapping force.
    • Cell spreading behaviors on hybrid nanopillar and nanohole arrays

      Wu, Xiaomin; Li, Li; Wang, Lu; Lei, Zecheng; Yang, Fan; Liu, Ri; Wang, Ying; Peng, Kuiqing; Wang, Zuobin; Wu X (IOP Publishing, 2021-11-05)
      Although nanopillars (NPs) provide a promising tool for capturing tumor cells, the effect of mixing NPs with other nanopatterns on cell behavior remains to be further studied. In this paper, a method of fabricating silicon nanoscale topographies by combining laser interference lithography with metal assisted chemical etching was introduced to investigate the behaviors and pseudopodia of A549 cells on the topologies. It was found that cells had a limited manner in spreading with small cell areas on the silicon nanopillar (SiNP) arrays, but a good manner in spreading with large cell areas on the silicon nanohole (SiNH) arrays. When on the hybrid SiNP/SiNH arrays, cells had medium cell areas and they arranged orderly along the boundaries of SiNPs and SiNHs, as well as 80% of cells displayed a preference for SiNPs over SiNHs. Furthermore, the lamellipodia and filopodia are dominant in the hybrid SiNP/SiNH and SiNP arrays, respectively, both of them are dominant in the SiNH arrays. In addition, the atomic force acoustic microscopy was also employed to detect the subsurface features of samples. The results suggest that the hybrid SiNP/SiNH arrays have a targeted trap and elongation effect on cells. The findings provide a promising method in designing hybrid nanostructures for efficient tumor cell traps, as well as regulating the cell behaviors and pseudopodia.
    • Cellular shear adhesion force measurement and simultaneous imaging by atomic force microscope

      Hou, Yu; Wang, Zuobin; Li, Dayou; Qiu, Renxi; Li, Yan; Jiang, Jinlan; Changchun University of Science and Technology; Chinses Academy of Sciences; University of Bedfordshire; Jilin University (Springer, 2017-01-06)
      This paper presents a sensitive and fast cellular shear adhesion force measurement method using an atomic force microscope (AFM). In the work, the AFM was used both as a tool for the imaging of cells on the nano-scale and as a force sensor for the measurement of the shear adhesion force between the cell and the substrate. After the cell imaging, the measurement of cellular shear adhesion forces was made based on the different positions of the cell on the nano-scale. Moreover, different pushing speeds of probe and various locations of cells were used in experiments to study their influences. In this study, the measurement of the cell adhesion in the upper portion of the cell is different from that in the lower portion. It may reveal that the cancer cells have the metastasis tendency after cultured for 16 to 20 hours, which is significant for preventing metastasis in the patients diagnosed with early cancer lesions. Furthermore, the cellular shear adhesion forces of two types of living cancer cells were obtained based on the measurements of AFM cantilever deflections in the torsional and vertical directions. The results demonstrate that the shear adhesion force of cancer cells is twice as much as the same type of cancer cells with TRAIL. The method can also provide a way for the measurement of the cellular shear adhesion force between the cell and the substrate, and for the simultaneous exploration of cells using the AFM imaging and manipulation
    • Characteristics of near-nozzle spray development from a fouled GDI injector

      Zhou, Jianwei; Pei, Yiqiang; Peng, Zhijun; Zhang, Yanfeng; Qin, Jing; Wang, Li; Liu, Changwen; Zhang, Xiaoyu; Tianjin University; University of Bedfordshire; et al. (Elsevier Ltd, 2018-03-16)
      The near-nozzle spray development of a typical fouled gasoline direct injection (GDI) injector was investigated. The fouled injector had been used in a stratified-charge combustion GDI engine and showed typical characteristics, such as accumulated deposits inside and around the nozzles and a reduced flow rate of 2.9–5.7%. Back-illumination and Mie-scattering methods were employed in spray experiments, in conjunction with a high speed camera and a macro lens, to assess the near-nozzle spray behaviors. The experimental results show that at all injection pressures tested, the interaction between deposits and spray led to several poor spray behaviors during the full injection evolution, including spray distortion, residual fuel storage in the nozzles and deposits layer, liquid splashing, the formation of ligament and large droplets and tip wetting/dripping. These effects all may result in high soot emissions. The after-injection stage of the fouled injector produced more liquid ligaments than that of the new injector. It was also found that high injection pressures did not improve atomization during after-injection, nor reduce the amounts of ligaments and droplet clusters beyond the main spray boundary. The plume width and projected spray area of a single nozzle in the fouled injector were decreased by 5–7% and 17–20%, respectively, due to fuel flow losses. The delays in the start of injection and end of injection were approximately 20 μs and 30–40 μs, respectively.
    • A closed-loop reciprocity calibration method for massive MIMO in terrestrial broadcasting systems

      Luo, Hua; Zhang, Yue; Huan, Li-Ke; Cosmas, John; Aggoun, Amar; University of Bedfordshire; Brunel University; Cobham Wireless (IEEE, 2016-09-22)
      Massive multi-input multioutput (MIMO) is believed to be an effective technique for future terrestrial broadcasting systems. Reciprocity calibration is one of the major practical challenges for massive MIMO systems operating in time-division duplexing mode. A new closed-loop reciprocity calibration method is investigated in this paper which can support online calibration with a higher accuracy compared to the existing methods. In the first part of the proposed method, an optimized relative calibration is introduced using the same structure of traditional relative calibration, but with less impaired hardware in the reference radio chain. In the second part, a test device (TD)-based calibration is proposed which makes online calibration possible. An experiment setup is built for the measurement of the base station hardware impairments and TD-based calibration implementation. Simulation results and the error vector magnitude of UE received signal after calibration show that the performance of our proposed method is improved significantly compared to the existing relative calibration methods.
    • A compact size implantable antenna for bio-medical applications

      Malik, Nabeel A.; Ajmal, Tahmina; Sant, Paul; Ur-Rehman, Masood; University of Bedfordshire; University of Glasgow (Institute of Electrical and Electronics Engineers Inc., 2020-09-29)
      Implantable antennas play a vital role in implantable sensors and medical devices. In this paper, we present the design of a compact size implantable antenna for biomedical applications. The antenna is designed to operate in ISM band at 915 MHz and the overall size of the antenna is 4 imes 4 imes 0.3 mm {3}. A shorting pin is used to lower the operating frequency of the antenna. For excitation purpose a 50-ohm coaxial probe feed is used in the design. A superstrate layer is placed on the patch to prevent the direct contact between the radiating patch and body tissues. The antenna is simulated in skin layer model. The designed antenna demonstrates a gain of 3.22 dBi while having a-10 dB bandwidth of 240 MHz with good radiation characteristics at 915 MHz. The simulated results show that this antenna is an excellent candidate for implantable applications.
    • Comparative study on the macroscopic characteristics of gasoline and ethanol spray from a GDI injector under injection pressures of 10 and 60 MPa

      Li, Xiang; Li, Dayou; Liu, Jingyin; Ajmal, Tahmina; Aitouche, Abdel; Mobasheri, Raouf; Rybdylova, Oyuna; Pei, Yiqiang; Peng, Zhijun (ACS, 2022-03-04)
      To reduce particulate matter (PM) emissions from vehicles powered by gasoline direct injection (GDI) engines, increasing the fuel injection pressure has been one promising approach. However, a comparison of macroscopic characteristics between gasoline and ethanol from a GDI injector under an ultrahigh injection pressure of more than 50 MPa has not been reported. The experimental study presented in this paper can provide some new and valuable information about comparing and analyzing the macroscopic characteristics of gasoline and ethanol spray from a GDI injector in both front and side views under injection pressures of 10 and 60 MPa. The experimental results show that compared to ethanol, gasoline spray has a slight advantage in LS (penetration of whole spray), LC (penetration of core region of spray), θS (spray cone angle), and RI (irregularity of spray boundary) under both PI (injection pressure) = 10 MPa and PI = 60 MPa, which would promote a more homogeneous mixture of air and fuel. Furthermore, the advantage of gasoline in θS is more pronounced under PI = 60 MPa. At the end of injection, SS (area of whole spray) of gasoline is around 2% larger than ethanol, while its advantage in SC (area of core region of spray) can be around 5%. With the increase of PI from 10 to 60 MPa, a marked increase of RS (the ratio of SC to SS) and RI indicates that atomization and air–fuel mixture homogeneity can be significantly improved for both gasoline and ethanol spray. Besides, a minor revision to the Dent model helps achieve a significant improvement in the prediction accuracy of LS for both gasoline and ethanol spray under injection pressures of 10 and 60 MPa.
    • Convexity characterization of virtual view reconstruction error in multi-view imaging

      Velisavljević, Vladan; Dorea, Camilo; Chakareski, Jacob; de Queiroz, Ricardo (IEEE, 2017-09-22)
      Virtual view synthesis is a key component of multi-view imaging systems that enable visual immersion environments for emerging applications, e.g., virtual reality and 360-degree video. Using a small collection of captured reference viewpoints, this technique reconstructs any view of a remote scene of interest navigated by a user, to enhance the perceived immersion experience. We carry out a convexity characterization analysis of the virtual view reconstruction error that is caused by compression of the captured multi-view content. This error is expressed as a function of the virtual viewpoint coordinate relative to the captured reference viewpoints. We derive fundamental insights about the nature of this dependency and formulate a prediction framework that is able to accurately predict the specific dependency shape, convex or concave, for given reference views, multi-view content and compression settings. We are able to integrate our analysis into a proof-of-concept coding framework and demonstrate considerable benefits over a baseline approach.
    • Cooled solar PV panels for output energy efficiency optimisation

      Peng, Zhijun; Herfatmanesh, Mohammad R.; Liu, Yiming; University of Bedfordshire; University of Hertfordshire (Elsevier, 2017-07-10)
      As working temperature plays a critical role in influencing solar PV’s electrical output and efficacy, it is necessary to examine possible way for maintaining the appropriate temperature for solar panels. This research is aiming to investigate practical effects of solar PV surface temperature on output performance, in particular efficiency. Experimental works were carried out under different radiation condition for exploring the variation of the output voltage, current, output power and efficiency. After that, the cooling test was conducted to find how much efficiency improvement can be achieved with the cooling condition. As test results show the efficiency of solar PV can have an increasing rate of 47% with the cooled condition, a cooling system is proposed for possible system setup of residential solar PV application. The system performance and life cycle assessment suggest that the annual PV electric output efficiencies can increase up to 35%, and the annual total system energy efficiency including electric output and hot water energy output can increase up to 107%. The cost payback time can be reduced to 12.1 years, compared to 15 years of the baseline of a similar system without cooling sub-system.
    • Design and study of a circular polarised conical-disc-backed spiral antenna for X-Band applications

      Ur-Rehman, Masood; Safdar, Ghazanfar Ali; Yang, Xiaodong; Chen, Xiaodong; University of Bedfordshire; Xidian University; Queen Mary University of London (IEEE, 2017-10-02)
      Design of a conical-disc-backed circular-polarized Archimedean single-arm spiral antenna is presented in this paper. The antenna operation covers the X -band frequencies ranging from 8 to 12 GHz. The antenna makes use of a very simple structure having the single-arm spiral backed by a cone-shaped metallic disc to achieve high gain, circular polarization, and unidirectional symmetric radiation near the boresight. The diameter of the antenna only measures to 40 mm. The simulated and measured results show that the antenna has a very good impedance matching (better than −10 dB), good right-hand circular polarization (with an axial ratio of ≤3 dB) throughout the frequency range of interest, and offers a maximum peak gain of 11.4 dBiC. The presented S11 response and radiation pattern results also show that the antenna offers excellent performance in the X -band with no need of a balun. Antenna usefulness is also established through a detailed parametric study and comparison with a traditional flat disc structure. Compact size, simple design, wide range, and high gain make the proposed antenna design a good choice for radar, terrestrial communications, and satellite/aerospace communications applications.
    • Determination of beam incidence conditions based on the analysis of laser interference patterns

      Wang, Dapeng; Wang, Zuobin; Yue, Yong; Yu, Juncai; Tan, Chunlei; Li, Dayou; Qiu, Renxi; Maple, Carsten; Changchun University of Science and Technology; University of Bedfordshire; et al. (Elsevier GmbH, 2015-07-17)
      Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He-Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications.
    • Dissolved oxygen forecasting in aquaculture: a hybrid model approach

      Eze, Elias Chinedum; Ajmal, Tahmina; University of Bedfordshire (MDPI AG, 2020-10-12)
      Dissolved oxygen (DO) concentration is a vital parameter that indicates water quality. We present here DO short term forecasting using time series analysis on data collected from an aquaculture pond. This can provide the basis of data support for an early warning system, for an improved management of the aquaculture farm. The conventional forecasting approaches are commonly characterized by low accuracy and poor generalization problems. In this article, we present a novel hybrid DO concentration forecasting method with ensemble empirical mode decomposition (EEMD)-based LSTM (long short-term memory) neural network (NN). With this method, first, the sensor data integrity is improved through linear interpolation and moving average filtering methods of data preprocessing. Next, the EEMD algorithm is applied to decompose the original sensor data into multiple intrinsic mode functions (IMFs). Finally, the feature selection is used to carefully select IMFs that strongly correlate with the original sensor data, and integrate into both inputs for the NN. The hybrid EEMD-based LSTM forecasting model is then constructed. The performance of this proposed model in training and validation sets was compared with the observed real sensor data. To obtain the exact evaluation accuracy of the forecasted results of the hybrid EEMD-based LSTM forecasting model, four statistical performance indices were adopted: mean absolute error (MAE), mean square error (MSE), root mean square error (RMSE), and mean absolute percentage error (MAPE). Results are presented for the short term (12-h) and the long term (1-month) that are encouraging, indicating suitability of this technique for forecasting DO values.
    • A dynamic feedback algorithm of AFM based on cell morphology changes

      Cheng, Can; Wang, Xinyue; Dong, Jianjun; Liu, Zimin; Wang, Zuobin; Changchun University of Science and Technology; University of Bedfordshire (IEEE, 2021-11-18)
      The atomic force microscope (AFM) used in biological research as a powerful tool has been for many years. However, the imaging of living cells is still a problem as the sample is too high and too soft to obtain their accurate morphologies. Especially in the high-speed scanning mode, AFM does not have enough judgments to make accurate measurements at the down part of the sample. In this study, we propose an improved control method to improve the image quality of living human colon cancer cells (SW480) especially in the down part during the scanning.
    • Effect of astragalus polysaccharides on cancer cells studied by AFM

      Lu, Zhengcheng; Wang, Zuobin; Li, Dayou; Zhu, Wenyu; Wang, Rui; Qu, Kaige; Yan, Jin; University of Bedfordshire; Changchun University of Science and Technology (IEEE, 2021-11-18)
      As a traditional Chinese medicine, astragalus and its products are used in cancer treatment aiming to reduce the side effects of chemotherapy. Cells are the most basic unit of living organisms, and AFM directly obtains information from living cells on the micro/nano scale. Therefore, the use of AFM to study the interaction between astragalus and cells is conducive to a full range of drug efficacy evaluation and provides a new way for drug development. In this paper, astragalus polysaccharides were extracted from astragalus, which were diluted into solutions of different concentrations. Combined with the MTT experiment, the effects of Astragalus polysaccharide on cancer cells and benign cells were studied by AFM.
    • Effect of different trypsin concentrations on SMCC-7721 cell adhesion

      Yan, Jin; Tian, Liguo; Xie, Chenchen; Liu, Yan; Lu, Zhengcheng; Wang, Zuobin; Changchun University of Science and Technology; University of Bedfordshire (International Journal of Pharma Medicine and Biological Sciences, 2021-07-03)
      In this work, living human liver cancer cells (SMCC-7721) were exposed to the trypsin solution at the concentrations of 1.5 mg/ml, 2.0 mg/ml, 2.5 mg/ml, 3.0 mg/ml, 3.5 mg/ml and 4.0 mg/ml, respectively. After 2 min of dosing time, the physical and mechanical properties of the cells were detected by Atomic Force Microscope (AFM). With the increase of the trypsin concentration, the adhesion force between the cell and the probe gently decreased. The maximum lateral deflection voltage variation of the probe, which reflected the maximum external force that kept the cells attached to the substrate, was significantly reduced. This work indicates that we may change the cell morphology and regulate the mechanical properties of cells by controlling the concentration of trypsin solution to treat cells, which has important implications for bioengineering and cell manipulation.
    • Effect of SMMC-7721-derived exosomes on hepatocytes studied by AFM

      Ju, Tuoyu; Yang, Fan; Wang, Ying; Song, Zhengxun; Xu, Hongmei; Chen, Yujuan; Wang, Zuobin; Changchun University of Science and Technology; University of Bedfordshire (IEEE, 2021-11-18)
      Exosomes play an important role in the early diagnosis and development of hepatocellular carcinoma (HCC). In the past, researchers mainly studied the contents of exosomes and the biological mechanism on cells, but the changes of mechanical properties of cells caused by exosomes are not clear. In this study, the changes of mechanical properties of hepatocytes (L-02) co-cultured with exosomes (7721-exos) derived from HCC (SMMC-7721) with low metastatic ability were studied. The 7721-exos were able to promote the proliferation and rearrange the cytoskeleton of L-02 cells. The atomic force microscopy measurement results showed that the height was increased, the adhesion and the elastic modulus were reduced. The effect was concentration dependent. The changes of cell mechanical properties induced by exosomes were of great significance for further studying the mechanism of exosomes.
    • Effects of injection rate profile on combustion process and emissions in a diesel engine

      Bai, Fuqiang; Zhang, Zuowei; Du, Yongchen; Zhang, Fan; Peng, Zhijun; Tianjin University; University of Hertfordshire; University of Bedfordshire (Hindawi, 2017-06-21)
      When multi-injection is implemented in diesel engine via high pressure common-rail injection system, changed interval between injection pulses can induce variation of injection rate profile for sequential injection pulse, though other control parameters are same. Variations of injection rate shape which influence the air-fuel mixing and combustion process will be important for designing injection strategy. In this research, CFD numerical simulations using KIVA-3V were conducted for examining the effects of injection rate shape on diesel combustion and emissions. After the model was validated by experimental results, five different shapes (including rectangle, slope, triangle, trapezoid and wedge) of injection rate profiles were investigated. Modelling results demonstrate that injection rate shape can have obvious influence on heat release process and heat release traces which cause different combustion process and emissions. It is observed that the baseline - rectangle (flat) shape of injection rate can have better balance between NOx and soot emissions than other investigated shapes. As wedge shape brings about the lowest NOx emissions due to retarded heat release, it produces highest soot emissions among five shapes. Trapezoid shape has the lowest soot emissions, while its NOx is not the highest one. The highest NOx emissions was produced by triangle shape due to higher peak injection rate.
    • Effects of laser fluence on silicon modification by four-beam laser interference

      Zhao, Le; Wang, Zuobin; Zhang, Jinjin; Yu, Miao; Li, Siwei; Li, Dayou; Yue, Yong; Changchun University of Science and Technology; University of Bedfordshire; Jiaotong-Liverpool University (American Institute of Physics Inc., 2015-12-17)
      This paper discusses the effects of laser fluence on silicon modification by four-beam laser interference. In this work, four-beam laser interference was used to pattern single crystal silicon wafers for the fabrication of surface structures, and the number of laser pulses was applied to the process in air. By controlling the parameters of laser irradiation, different shapes of silicon structures were fabricated. The results were obtained with the single laser fluence of 354 mJ/cm, 495 mJ/cm, and 637 mJ/cm, the pulse repetition rate of 10 Hz, the laser exposure pulses of 30, 100, and 300, the laser wavelength of 1064 nm, and the pulse duration of 7-9 ns. The effects of the heat transfer and the radiation of laser interference plasma on silicon wafer surfaces were investigated. The equations of heat flow and radiation effects of laser plasma of interfering patterns in a four-beam laser interference distribution were proposed to describe their impacts on silicon wafer surfaces. The experimental results have shown that the laser fluence has to be properly selected for the fabrication of well-defined surface structures in a four-beam laser interference process. Laser interference patterns can directly fabricate different shape structures for their corresponding applications.
    • Effects of water injection strategies on oxy-fuel combustion characteristics of a dual-injection spark ignition engine

      Li, Xiang; Pei, Yiqiang; Li, Dayou; Ajmal, Tahmina; Rana, Khaqan-Jim; Aitouche, Abdel; Mobasheri, Raouf; Peng, Zhijun; University of Bedfordshire; Tianjin University; et al. (MDPI, 2021-08-26)
      Currently, global warming has been a serious issue, which is closely related to anthropogenic emission of Greenhouse Gas (GHG) in the atmosphere, particularly Carbon Dioxide (CO2). To help achieve carbon neutrality by decreasing CO2 emissions, Oxy-Fuel Combustion (OFC) technology is becoming a hot topic in recent years. However, few findings have been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engines. This work numerically explores the effects of Water Injection (WI) strategies on OFC characteristics in a practical dual-injection engine, including GDI (only using GDI), P50-G50 (50% PFI and 50% GDI) and PFI (only using PFI). The findings will help build a conceptual and theoretical foundation for the implementation of OFC technology in dual-injection SI engines, as well as exploring a solution to increase engine efficiency. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. Ignition delay (θF) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (θC) of PFI is a bit shorter than that of GDI and P50-G50. There is a small benefit to BSFC under a low water-fuel mass ratio (Rwf). However, with the further increase of Rwf from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As WI timing (tWI) postpones to around −30 °CA under the conditions of Rwf ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of maximum cylinder pressure (Pmax) and combustion phasing is less affected by WI temperature (TWI) compared to the effects of Rwf or tWI. BSFC just has a small decline with the increase of TWI from 298 K to 368 K regardless of the injection strategy. Consequently, appropriate WI strategies are beneficial to OFC combustion in a dual-injection SI engine, but the benefit in fuel economy is limited.
    • Electrical conductivity measurement of λ DNA molecules by conductive atomic force microscopy

      Wang, Ying; Xie, Ying; Gao, Mingyan; Zhang, Wenxiao; Liu, Lanjiao; Qu, Yingmin; Wang, Jiajia; Hu, Cuihua; Song, Zhengxun; Wang, Zuobin; et al. (IOP Publishing, 2021-11-08)
      Conductive atomic force microscopy (C-AFM) is a powerful tool used in the microelectronics analysis by applying a certain bias voltage between the conducting probe and the sample and obtaining the electrical information of sample. In this work, the surface morphological information and current images of the lambda DNA (λ DNA) molecules with different distributions were obtained by C-AFM. The 1 and 10 ng μl−1 DNA solutions were dripped onto mica sheets for making randomly distributed DNA and DNA network samples, and another 1 ng μl−1 DNA sample was placed in a DC electric field with a voltage of 2 V before being dried for stretching the DNA sample. The results show that the current flowing through DNA networks was significantly higher than the stretched and random distribution of DNA in the experiment. The I–V curve of DNA networks was obtained by changing the bias voltage of C-AFM from −9 to 9 V. The currents flowing through stretched DNA at different pH values were studied. When the pH was 7, the current was the smallest, and the current was gradually increased as the solution became acidic or alkaline.