There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Many types of nanoparticles (NPs) are tested for use in medical products, particularly in imaging and gene and drug delivery. For these applications, cellular uptake is usually a prerequisite and is governed in addition to size by surface characteristics such as hydrophobicity and charge. Although positive charge appears to improve the efficacy of imaging, gene transfer, and drug delivery, a higher cytotoxicity of such constructs has been reported. This review summarizes findings on the role of surface charge on cytotoxicity in general, action on specific cellular targets, modes of toxic action, cellular uptake, and intracellular localization of NPs. Effects of serum and intercell type differences are addressed. Cationic NPs cause more pronounced disruption of plasma-membrane integrity, stronger mitochondrial and lysosomal damage, and a higher number of autophagosomes than anionic NPs. In general, nonphagocytic cells ingest cationic NPs to a higher extent, but charge density and hydrophobicity are equally important; phagocytic cells preferentially take up anionic NPs. Cells do not use different uptake routes for cationic and anionic NPs, but high uptake rates are usually linked to greater biological effects. The different uptake preferences of phagocytic and nonphagocytic cells for cationic and anionic NPs may influence the efficacy and selectivity of NPs for drug delivery and imaging.

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The role of surface charge in cellular uptake and cytotoxicity of medical nanoparticles.

Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Author(s): Vogel, Alfred; Venugopalan, Vasan | Abstract: The mechanisms of pulsed laser ablation of biological tissues were studied. The transiently empty space created between the fiber tip and the tissue surface improved the optical transmission to the target and thus increased the ablation efficiency. It was found that the structure and morphology also affect the energy transport among tissue constituents.

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Mechanisms of pulsed laser ablation of biological tissues.

Die thermische Unkrautbekampfung mit Abflamm-, Heiswasser-/Heisdampf- und Heisschaumgeraten ist hinsichtlich eines punktuellen Einsatzes begrenzt. Dies ist insbesondere nachteilig fur die Unkrautbekampfung in Kulturbestanden, weil die thermische Schadigung hier raumlich wirkt. Daher ist ein alternatives Werkzeug erforderlich, z. B. die Lasertechnik. Bei der Laserapplikation konnen Laserparameter online auf die erkannte Unkrautsituation angepasst werden. Entsprechende Untersuchungen werden kooperativ am Fachgebiet Biosystem- und Gartenbautechnik der Leibniz Universitat Hannover sowie am Laser Zentrum Hannover durchgefuhrt.

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Untersuchungen zur Absorption und Applikation von Laserstrahlung zur Unkrautbekämpfung

Nanoparticles are known to cause adverse health effects. But the generation of nanoparticles cannot be avoided during
laser machining, especially ultrashort-pulsed laser ablation which releases a high share of nanoparticles.
The nanoparticulate size fractions emitted during picosecond (ps) laser ablation are compared with those released during
femtosecond (fs) laser ablation using steel, zirconia and brass. At the same pulse energy, fs pulses release similar share
of nanoparticles (>80%) in the aerosol fraction, with fs compared to ps generating a far higher share of ultrasmall (7 nm)
sized particles during machining of metals and ceramics. The frequency maximum corresponds to the particle size of
50 nm independently of the ablated material and applied pulse duration. During ps laser ablation the absolute
nanoparticle emission rate is higher than during fs laser ablation, whereas the emission rate per pulse is two magnitudes
lower. Finally, the nanoparticle emission rates and its nanoparticle surface equivalent for ps and fs laser micromachining
of metal and ceramic are compared with inflammatory thresholds derived from toxicology studies. It would take more
than 6.500 working days to exceed this theoretical threshold of inflammation during laser operation at 0.5-2W and at
least 260 working days using high-power lasers.

Health risks of nanoparticulate emissions during femtosecond and picosecond pulsed laser machining

Electrophoretic deposition (EPD) of platinum nanoparticles (PtNPs) on platinum-iridium (Pt-Ir) neural electrode surfaces is a promising strategy to tune the impedance of electrodes implanted for deep brain stimulation in various neurological disorders such as advanced Parkinson's disease and dystonia. However, previous results are contradicting as impedance reduction was observed on flat samples while in three-dimensional (3D) structures, an increase in impedance was observed. Hence, defined correlations between coating properties and impedance are to date not fully understood. In this work, the influence of direct current (DC) and pulsed-DC electric fields on NP deposition is systematically compared and clear correlations between surface coating homogeneity and in vitro impedance are established. The ligand-free NPs were synthesized via pulsed laser processing in liquid, yielding monomodal particle size distributions, verified by analytical disk centrifugation (ADC). Deposits formed were quantified by UV-vis supernatant analysis and further characterized by scanning electron microscopy (SEM) with semiautomated interparticle distance analyses. Our findings reveal that pulsed-DC electric fields yield more ordered surface coatings with a lower abundance of particle assemblates, while DC fields produce coatings with more pronounced aggregation. Impedance measurements further highlight that impedance of the corresponding electrodes is significantly reduced in the case of more ordered coatings realized by pulsed-DC depositions. We attribute this phenomenon to the higher active surface area of the adsorbed NPs in homogeneous coatings and the reduced particle-electrode electrical contact in NP assemblates. These results provide insight for the efficient EPD of bare metal NPs on micron-sized surfaces for biomedical applications in neuroscience and correlate coating homogeneity with in vitro functionality.

Comparing Direct and Pulsed-Direct Current Electrophoretic Deposition on Neural Electrodes: Deposition Mechanism and Functional Influence.

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Advances in pulsed laser synthesis of nanoparticles in liquids

The invention relates to a method and to a device for producing conjugates comprising or consisting of a metallic nanoparticulate component and an organic component. Said method enables activated or reactive nanoparticles containing metal to be produced by irradiating a metal body with a laser beam and prevents the modification and damage of organic components of said conjugates by laser irradiation. Said nanoparticulate metallic component comprises plasmon resonant metal. According to the invention, the claimed method of production enables particles having a metal centre and a metal-oxide covering to be produced, in particular when using a carrier fluid containing oxygen, e.g. alcohol or water.

Stephan Barcikowski

Papers

Untersuchungen zur Absorption und Applikation von Laserstrahlung zur Unkrautbekämpfung

Health risks of nanoparticulate emissions during femtosecond and picosecond pulsed laser machining

Comparing Direct and Pulsed-Direct Current Electrophoretic Deposition on Neural Electrodes: Deposition Mechanism and Functional Influence.

Advances in pulsed laser synthesis of nanoparticles in liquids

Method and device for producing metal-containing organic compounds