Comprehensive Investigation of the Temperature-Dependent Electromechanical Behaviors of Carbon Nanotube/Polymer Composites.

The performances of flexible piezoresistive sensors based on polymer nanocomposites are significantly affected by the environmental temperature; therefore, comprehensively investigating the temperature-dependent electromechanical response behaviors of conductive polymer nanocomposites is crucial for developing high-precision flexible piezoresistive sensors in a wide-temperature range. Herein, carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites widely used for flexible piezoresistive sensors were prepared, and then the temperature-dependent electrical, mechanical, and electromechanical properties of the optimized CNT/PDMS composite in the temperature range from -150 to 150 °C were systematically investigated. At a low temperature of -150 °C, the CNT/PDMS composite becomes brittle with a compressive modulus of ∼1.2 MPa and loses its elasticity and reversible sensing capability. At a high temperature (above 90 °C), the CNT/PDMS composite softens, shows a fluid-like mechanical property, and loses its reversible sensing capability. In the temperature range from -60 to 90 °C, the CNT/PDMS composite exhibits good elasticity and reversible sensing behaviors and its modulus, resistivity, and sensing sensitivity decrease with an increasing temperature. At room temperature (30 °C), the CNT/PDMS composite exhibits better mechanical and piezoresistive stability than those at low and high temperatures. Given that environmental temperature changes have significant effects on the sensing performances of conductive polymer composites, the effect of ambient temperature changes must be considered when flexible piezoresistive sensors are designed and fabricated.

Exploring the formation mechanism of fine particles in an ex-heavily polluted Northwestern city, China.

Fine particle pollution is still a severe issue in the northwestern region of China where the formation mechanism of which remains ambiguous due to the limited studies there. In this study, a comprehensive study on the chemical composition and sources of PM2.5 at an ex-heavily polluted northwestern city was conducted, based on filter sampling data obtained from three consecutive winter campaigns during 2020-2022. The average PM2.5 during the three winter campaigns were 170.9 ± 66.4, 249.0 ± 75.7, and 200.9 ± 47.6 µg/m3, respectively, with the daily maximum value of PM2.5 exceeds 400 µg/m3 under stagnant meteorological conditions charactered by high relative humidity (>60 %) and low wind speed (<1 m/s). The major chemical components in PM2.5 were found to be inorganic aerosol (55.2 %) that mainly constituted by sulfate (24.2 %), and mineral dust (14.9 %); while the carbonous species contributed a minor fraction (∼13 %). In addition, (NH4)2SO4 and NH4NO3 were the dominate contributors to appearance of low visibility (<3 km) which together accounting for over 85 % of light extinction coefficient (bext) during heavy polluted period. Source appointment of fine particles was then conducted by applying the positive matrix factorization method, and the primary sources were resolved to be coal combustion (27.7 %) and biomass burning (18.6 %), followed by industrial dust (16.2 %), residential combustion (15.3 %), traffic emissions (11.9 %) and dust aerosol (10.4 %). To explore the potential formation mechanism of fine particle pollution, the chemical evolution pattern combined with gaseous pollutants and meteorological parameters were further analyzed, which refine the important role of primary emissions in the forming of high sulfate aerosol loading, while secondary formation was largely suppressed during the winter period that totally different from those reported in the developed regions of China, thus indicating more effort should be paid on the reduction of primary particles emissions in the northwestern cities than on its gaseous percussors.

Multiresponsive Ti3C2Tx MXene-Based Actuators Enabled by Dual-Mechanism Synergism for Soft Robotics.

Multiresponsive and high-performance flexible actuators with a simple configuration, high mechanical strength, and low-power consumption are highly desirable for soft robotics. Here, a novel mechanically robust and multiresponsive Ti3C2Tx MXene-based actuator with high actuation performance via dual-mechanism synergistic effect driven by the hygroexpansion of bacterial cellulose (BC) layer and the thermal expansion of biaxially oriented polypropylene (BOPP) layer is developed. The actuator is flexible and shows an ultrahigh tensile strength of 195 MPa. Unlike the conventional bimorph-structured actuators based on a single-mechanism, the actuator developed provides a favorable architecture for dual-mechanism synergism, resulting in exceptionally reversible actuation performance under electricity and near-infrared (NIR) light stimuli. Typically, the developed actuator can produce the largest bending angle (∼400°) at the lowest voltage (≤4 V) compared with that reported previously for single mechanism soft actuators. Furthermore, the actuator also can be driven by a NIR light at a 2 m distance, displaying an excellent long-distance photoresponsive property. Finally, various intriguing applications are demonstrated to show the great potential of the actuator for soft robotics.

Multifunctional Polyurethane Composite Foam with Outstanding Anti-impact Capacity for Soft Body Armors.

Herein, a multifunctional polyurethane (PU) composite foam with a hierarchical structure is fabricated by dip-coating a carbon nanotube/shear-thickening gel (CNT/STG) and spray-coating nano-SiO2/STG on PU foam. The prepared nano-SiO2/CNT/STG@PU (SCS@PU) composite foam is lightweight, highly compressive, electrically conductive, superhydrophobic, and impact-energy absorptive. As a result, it possesses an excellent sensing ability to compression with a stable response up to 80% strain, an outstanding linearity of R2 > 0.99, and a wide response frequency of 0.01 to 1 Hz; it can also be used for effectively detecting impact force and sensing various human motions. Moreover, the superhydrophobicity with a water contact angle up to 154° of SCS@PU composite foam endows it with an excellent resistance to hazardous liquids (strong acid and alkali) to ensure its service reliability under harsh circumstances. In particular, the SCS@PU exhibits an outstanding anti-impact capability with an impact force attenuation rate of SCS@PU as high as 81%. Finally, its applications as soft body armors are demonstrated in protecting a wearer wearing a helmet with the SCS@PU as liner and using the SCS@PU as a smart kneecap against impact. On consideration of its excellent strain-sensing ability, superhydrophobicity, and outstanding anti-impact capability, the multifunctional SCS@PU composite foam developed is promising for personal safety protection.

Superstrong, Lightweight, and Exceptional Environmentally Stable SiO2@GO/Bamboo Composites.

Development of lightweight structural materials from fast-growing bamboos is of great significance to building a sustainable society. However, previously developed structural bamboos by delignification combined with densification would easily fail under large external loading after exposure to water due to structure collapse, severely limiting their practical applications. Here, we demonstrate an ultrastrong and exceptional environmentally stable bamboo composite consisting of a graphene oxide (GO)/bamboo core and hierarchical SiO2 protection layer. The GO/bamboo composite exhibits ultrahigh tensile strength (641.6 MPa), superb flexural strength (428.4 MPa), and excellent toughness (17.5 MJ/m3), which are increased by about 480, 250, and 360% compared with natural bamboo, respectively. As a result, the specific tensile strength of the GO/bamboo composite is up to 513.3 MPa·cm3/g due to its low density (1.25 g/cm3), outperforming engineering structural materials such as aluminum alloys, steels, and titanium alloys. These large improvements benefit from the well-preserved bamboo scaffold and the strong hydrogen bonds between bamboo fibers and GO nanosheets. On the other hand, the SiO2@GO/bamboo composite shows superhydrophobicity due to the construction of hierarchical SiO2 layers, which endows it with outstanding water resistance. Moreover, the bamboo composite shows an ultralow coefficient of thermal expansion (≈2.3 × 10-6 K-1), indicating its excellent dimensional stability. Considering the ultrahigh mechanical performance and outstanding environmental stability, the developed lightweight SiO2@GO/bamboo composite is hopeful to be a green and sustainable structural material for practical engineering applications.

A micromachined force sensing apparatus and method for human engineered cardiac tissue and induced pluripotent stem cell characterization.

Induced pluripotent stem cell derived-cardiomyocytes (iPSC-CMs) have great potential for cell therapy, drug assessment, and for understanding the pathophysiology and genetic underpinnings of cardiac diseases. Contraction forces are one of the most important characteristics of cardiac function and are predictors of healthy and diseased states. Cantilever techniques, such as atomic force microscopy, measure the vertical force of a single cell, while systems designed to more closely resemble the physical heart function, such as engineered cardiac tissue held by end-posts, measure the axial force. One important question is how do these two force measurements correlate? By establishing a correlation of the axial and vertical force, we will be one step closer in being able to use single cell iPSC-CMs as models. A novel micromachined sensor for measuring force contractions of engineered tissue has been developed. Using this novel sensor, a correlation between axial force and vertical force is experimentally established. This finding supports the use of vertical measurements as an alternative to tissue measurements.

Modified adaptive filter for digital subdivision of a four-frequency differential laser gyro.

This study represents a modified adaptive filter to suppress the beat noise of four-frequency differential laser gyro (FFDLG), which greatly affects the result of the eightfold digital subdivision. By constructing the demodulated signal model of FFDLG, the influence of beat noise to digital subdivision is analyzed. Based on the least mean square adaptive algorithm, a process of signal reconstruction and dead-zone operator of error are adopted in the modified adaptive algorithm. When implemented on a field-programmable gate array chip, the filter replaces the multiplication with 2:1 multiplexer to reduce the complexity of algorithm and resources in circuit. This circuit effectively suppresses the beat noise of the demodulated signal without changing the optical structure of the FFDLG and increases the signal-to-noise ratio from 20 dB to about 40 dB, which is conducive to improving the performance of the FFDLG.

High-Performance Fiber-Film Hybrid-Structured Wearable Strain Sensor from a Highly Robust and Conductive Carbonized Bamboo Aerogel.

Bamboo, one of the most abundant biomaterials, has been used as a building material since ancient times; however, its application in functional materials has been rarely explored. Herein, a highly robust and conductive carbonized bamboo aerogel (CBA) is obtained from the natural bamboo through a simple three-step process of pulp oxidization, freeze-drying, and carbonization. The CBA obtained shows not only a low density of 0.02 g/cm3 but also a high conductivity of 6.42 S/m and remarkable elasticity with a maximum recoverable compressive strain of 60% due to its unique three-dimensional (3D) network randomly stacked with the hybrid structure of carbonized bamboo fibers and films. After encapsulation with silicone resin, the CBA/silicone composite prepared exhibits excellent flexibility and stretchability with a low Young's modulus (0.09 MPa) and a large failure strain (275%). Importantly, the CBA/silicone composite also offers remarkable strain-sensing performance with a maximum gauge factor of 30.6, a short responsive time of 50 ms, and a stable response to cyclic loading over 1000 cycles, which is comparable to those of the piezoresistive composites based on expensive nanomaterials. Moreover, the CBA/silicone composite demonstrates the capability as a wearable strain sensor for human motion recognition comprising finger bending, breathing, and throat movement. Considering the green and sustainable nature of bamboo as a raw material, combined with the excellent piezoresistive performance, low production cost, and simple preparation process, the flexible strain sensors with CBA/silicone composite as a sensing element are promising in wearable electronic devices, personalized healthcare, and artificial intelligence systems.

Isolation and identification of Singapore grouper iridovirus Hainan strain (SGIV-HN) in China.

In recent years, with the rapid development of marine farming activities, outbreaks of viral diseases have affected the grouper aquaculture industry, causing heavy economic losses. Singapore grouper iridovirus (SGIV) is one of the most important viruses causing disease in fish. In the present study, we isolated and identified a virus from diseased groupers by coculturing the affected tissue cells with grouper spleen cells. The genome of the isolated virus shared 99.83% nucleotide sequence homology with those of SGIV reference strains in the GenBank database. The virus clustered with SGIV on an evolutionary tree constructed based on "major capsid protein" (MCP) amino acid sequences, so it was designated 'Singapore grouper iridovirus Hainan' (SGIV-HN). To evaluate the pathogenic potential of SGIV-HN in fish, orange-spotted groupers were infected by intraperitoneal injection with the virus. Infected groupers began to die from the fourth day after infection, and survivors tended to be stable by the eighth day. The death rate was 83.33%. In a mock-infected control group, only two fish died, and the mortality rate was 6.67%. Dissection showed that the fish had enlarged spleens with hemorrhage, and enlarged cells were visible with Giemsa staining. This is the first report of isolation of SGIV from naturally infected fish in China, and we show that SGIV-HN is highly infectious, causing massive deaths in groupers.

Bioinspired Flexible and Highly Responsive Dual-Mode Strain/Magnetism Composite Sensor.

The mimicry of human skin to detect both oncoming and physical-contacting object is of great importance in the fields of manufacturing, artificial robots and vehicles, etc. Herein, a novel bioinspired flexible and highly responsive dual-mode strain/magnetism composite sensor, which works via both contact and contactless modes, is first fabricated by incorporating Fe3O4/silicone system into a carbon fiber aerogel (CFA). The distance dependence of magnetic field endorses the CFA/Fe3O4/silicone composite possible for spatial sensing due to the introduction of Fe3O4 magnetic nanoparticles. As a result, the as-prepared flexible sensor exhibits precise and real-time response not only to direct-contact compression as usual but also to contactless magnetic field in a wide frequency range from 0.1 to 10 Hz, achieving the maximum variance of 68% and 86% in relative electrical resistance, respectively. The contact and contactless sensing modes of the strain/magnetism sensor are clearly demonstrated by recording the speeds of bicycle riding and walking, respectively. Interestingly, this dual-mode composite sensor exhibits the capacity of identifying the contact and contactless state, which is the first report for flexible sensors. The current protocol is eco-friendly, facile, and thought-provoking for the fabrication of multifunctional sensors.

A wearable strain sensor based on a carbonized nano-sponge/silicone composite for human motion detection.

Melamine sponge, also known as nano-sponge, is widely used as an abrasive cleaner in our daily life. In this work, the fabrication of a wearable strain sensor for human motion detection is first demonstrated with a commercially available nano-sponge as a starting material. The key resistance sensitive material in the wearable strain sensor is obtained by the encapsulation of a carbonized nano-sponge (CNS) with silicone resin. The as-fabricated CNS/silicone sensor is highly sensitive to strain with a maximum gauge factor of 18.42. In addition, the CNS/silicone sensor exhibits a fast and reliable response to various cyclic loading within a strain range of 0-15% and a loading frequency range of 0.01-1 Hz. Finally, the CNS/silicone sensor as a wearable device for human motion detection including joint motion, eye blinking, blood pulse and breathing is demonstrated by attaching the sensor to the corresponding parts of the human body. In consideration of the simple fabrication technique, low material cost and excellent strain sensing performance, the CNS/silicone sensor is believed to have great potential in the next-generation of wearable devices for human motion detection.

Flexible wire-shaped strain sensor from cotton thread for human health and motion detection.

In this work, a wire-shaped flexible strain sensor was fabricated by encapsulating conductive carbon thread (CT) with polydimethylsiloxane (PDMS) elastomer. The key strain sensitive material, CT, was prepared by pyrolysing cotton thread in N2 atmosphere. The CT/PDMS composite wire shows a typical piezo-resistive behavior with high strain sensitivity. The gauge factors (GF) calculated at low strain of 0-4% and high strain of 8-10% are 8.7 and 18.5, respectively, which are much higher than that of the traditional metallic strain sensor (GF around 2). The wire-shaped CT/PDMS composite sensor shows excellent response to cyclic tensile loading within the strain range of 0-10%, the frequency range of 0.01-10 Hz, to up to 2000 cycles. The potential of the wire senor as wearable strain sensor is demonstrated by the finger motion and blood pulse monitoring. Featured by the low costs of cotton wire and PDMS resin, the simple structure and fabrication technique, as well as high performance with miniaturized size, the wire-shaped sensor based on CT/PDMS composite is believed to have a great potential for application in wearable electronics for human health and motion monitoring.

Multifunctional Wearable Device Based on Flexible and Conductive Carbon Sponge/Polydimethylsiloxane Composite.

Wearable devices that can be used to monitor personal health, track human motions, and provide thermotherapy, etc., are highly desired in personalized healthcare. In this work, a multifunctional wearable "wrist band" which works as both heater for thermotherapy and sensor for personal health and motion monitoring is fabricated from a flexible and conductive carbon sponge/polydimethylsiloxane (CS/PDMS) composite. The key functional material of the wrist band, namely, the conductive CS, is synthesized from waste paper by a freeze-drying and high-temperature pyrolysis process. When the wrist band works as a heater under 15 V, a stable temperature difference of 20 °C is achieved between the wrist band and the ambient. When the wrist band serves as a wearable strain sensor, the wrist band exhibits fast and repeatable response and excellent durability within the strain range of 0-20% and the working frequency of 0.01-10 Hz. Finally, the typical applications of the multifunctional wearable wrist band, as a heater for thermotherapy and a sensor for blood pulse, breathe, and walk monitoring, are demonstrated. Due to its low cost, high flexibility, moderate conductivity, and excellent strain sensibility, the as-prepared wearable device based on the CS/PDMS composite is promising to be applied for the provision of personal healthcare.

A microRNA from infectious spleen and kidney necrosis virus modulates expression of the virus-mock basement membrane component VP08R.

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the genus Megalocytivirus, family Iridoviridae. Infection of ISKNV is characterized by a unique pathological phenomenon in that the infected cells are attached by lymphatic endothelial cells (LECs). ISKNV mediates the formation of a virus-mock basement membrane (VMBM) structure on the surface of infected cells to provide attaching sites for LECs. The viral protein VP08R is an important component of VMBM. In this study, a novel ISKNV-encoded microRNA, temporarily named ISKNV-miR-1, was identified. ISKNV-miR-1 is complementary to the VP08R-coding sequence and can modulate VP08R expression through reducing its mRNA level. This suggests that formation of VMBM may be under fine regulation by ISKNV.

Litopenaeus vannamei Toll-interacting protein (LvTollip) is a potential negative regulator of the shrimp Toll pathway involved in the regulation of the shrimp antimicrobial peptide gene penaeidin-4 (PEN4).

The Toll-like receptor (TLR)-nuclear factor (NF)-κB signaling pathway is evolutionarily conserved from insects to mammals as a regulator of the expression of immune-related genes. In mammals, TLR-NF-κB signaling is tightly controlled because excessive activation of this pathway can result in severe damage to the host. The mammalian Toll-interacting protein (Tollip) has an important function in the negative regulation of this pathway, but no reports about invertebrate Tollip have been published to date. In this study, we cloned Litopenaeus vannamei Tollip (LvTollip) and investigated its function in the regulation of the NF-κB pathway-controlled antimicrobial peptide genes (AMPs). The LvTollip full-length cDNA is 1231bp long and contains an open reading frame of 813bp that encodes a 270-amino acid protein. LvTollip shares significant similarities to mammalian Tollips, which contain a centrally localized protein kinase C conserved region 2 (C2) domain and a C-terminal CUE domain. After challenges with the white spot syndrome virus (WSSV) or Vibrio alginolyticus, the expression levels of LvTollip were altered in the gill, hemocyte, hepatopancreatic, intestinal, and muscle tissues. In Drosophila S2 cells, LvTollip localized in the membrane and the cytoplasm and significantly inhibited the promoter activities of the NF-κB pathway-controlled AMP penaeidin-4 (PEN4). In LvTollip-knockdown shrimp, the expression level of AMP PEN4 was increased. However, the mortality rates of LvTollip-knockdown shrimp in response to WSSV or V. alginolyticus infections were not significantly different from those of the control group. Our results suggested that LvTollip might be involved in the negative regulation of PEN4 and that LvTollip expression was responsive to microbial infections.

Litopenaeus vannamei sterile-alpha and armadillo motif containing protein (LvSARM) is involved in regulation of Penaeidins and antilipopolysaccharide factors.

The Toll-like receptor (TLR)-mediated NF-κB pathway is tightly controlled because overactivation may result in severe damage to the host, such as in the case of chronic inflammatory diseases and cancer. In mammals, sterile-alpha and armadillo motif-containing protein (SARM) plays an important role in negatively regulating this pathway. While Caenorhabditis elegans SARM is crucial for an efficient immune response against bacterial and fungal infections, it is still unknown whether Drosophila SARM participates in immune responses. Here, Litopenaeus vannamei SARM (LvSARM) was cloned and functionally characterized. LvSARM shared signature domains with and exhibited significant similarities to mammalian SARM. Real-time quantitative PCR analysis indicated that the expression of LvSARM was responsive to Vibrio alginolyticus and white spot syndrome virus (WSSV) infections in the hemocyte, gill, hepatopancreas and intestine. In Drosophila S2 cells, LvSARM was widely distributed in the cytoplasm and could significantly inhibit the promoters of the NF-κB pathway-controlled antimicrobial peptide genes (AMPs). Silencing of LvSARM using dsRNA-mediated RNA interference increased the expression levels of Penaeidins and antilipopolysaccharide factors, which are L.vannamei AMPs, and increased the mortality rate after V. alginolyticus infection. Taken together, our results reveal that LvSARM may be a novel component of the shrimp Toll pathway that negatively regulates shrimp AMPs, particularly Penaeidins and antilipopolysaccharide factors.

[Preparation and identification of mouse anti-human CD52 functional antibody].

OBJECTIVE: To prepare and identify mouse anti-human CD52 antibody. METHODS: The RNA was extracted from Hut-78 cells. CD52 gene was amplified by RT-PCR. With the double-enzyme digestion, CD52 gene was cloned into pcDNA3.1(+) eukaryotic expression vector, named as pcDNA3.1(+)/CD52. We transfected the recombinant into CHO cell by Lipofectamine™ 2000. Stable transfected CHO cell line was established, and the CD52 expression in the transfected cells was detected by RT-PCR, FACS and immunocytochemical staining. BALB/c mice were immunized with synthetic peptide CD52. The titer of anti-CD52 serum was detected with indirect ELISA. Inhibition of leukemia LCL cell proliferation by immunized mouse serum was identified with MTS assay. RESULTS: The eukaryotic expression vector pcDNA3.1(+)/CD52 was constructed, stable transfected CHO cell line was established. High titer anti-CD52 antibody was identified. The immunized mouse serum inhibits proliferation of LCL cells by MTS assay. CONCLUSION: Preparation of functional antibody against CD52 and stable transfected CHO cell line have established successfully.

A piezo-thermal probe for thermomechanical analysis.

Thermomechanical analysis (TMA) is widely used to characterize materials and determine transition temperatures and thermal expansion coefficients. Atomic-force microscopy (AFM) microcantilevers have been used for TMA. We have developed a micromachined probe that includes two embedded sensors: one for measuring the mechanical movement of the probe (deflection) and another for providing localized heating. The new probe reduces costs and complexity and allow for portability thereby eliminating the need for an AFM. The sensitivity of the deflection element ((ΔR∕R)∕deflection) is 0.1 ppm∕nm and its gauge factor is 3.24. The melting temperature of naphthalene is measured near 78.5 °C.

Experimental evaluation of an adaptive Joule-Thomson cooling system including silicon-microfabricated heat exchanger and microvalve components.

This article reports the evaluation of a Joule-Thomson (JT) cooling system that combines two custom micromachined components-a Si/glass-stack recuperative heat exchanger and a piezoelectrically actuated expansion microvalve. With the microvalve controlling the flow rate, this system can modulate cooling to accommodate varying refrigeration loads. The perforated plate Si/glass heat exchanger is fabricated with a stack of alternating silicon plates and Pyrex glass spacers. The microvalve utilizes a lead zirconate titanate actuator to push a Si micromachined valve seat against a glass plate, thus modulating the flow passing through the gap between the valve seat and the glass plate. The fabricated heat exchanger has a footprint of 1 × 1 cm(2) and a length of 35 mm. The size of the micromachined piezoelectrically actuated valve is about 1 × 1 × 1 cm(3). In JT cooling tests, the temperature of the system was successfully controlled by adjusting the input voltage of the microvalve. When the valve was fully opened (at an input voltage of -30 V), the system cooled down to a temperature as low as 254.5 K at 430 kPa pressure difference between inlet and outlet at steady state and 234 K at 710 kPa in a transient state. The system provided cooling powers of 75 mW at 255 K and 150 mW at 258 K. Parasitic heat loads at 255 K are estimated at approximately 700 mW.

[Construction of eukaryotic expression vector of human CD34 and establishment of stably transfected cell line].

AIM: To construct eukaryotic expression vector of human CD34 and transfect it to 3T3 cells so as to establish stably transfected 3T3 cell line. METHODS: The RNA was extracted from KG1a. CD34 gene was amplified by RT-PCR. With the double-enzyme digestion, CD34 gene was cloned into pCI-neo eukaryotic expression vector, yielding pCI-CD34. The pCI-CD34 was transfected into 3T3 cell by electroporator. Stably transfected 3T3 cell line was established, and the CD34 expression in the transfected cells was detected by RT-PCR and FACS. RESULTS: The eukaryotic expression vector pCI-CD34 was constructed, and stably transfected 3T3 cell line was established. CONCLUSION: Construction of eukaryotic expression vector of CD34 and the establishment of stably transfected 3T3 cell line are helpful to preparation of anti-CD34 mAbs and further functional study of CD34.