Abstract. We evaluate the performance of the Single Particle Soot Photometer (SP2) and the Integrating Sphere/Integrating Sandwich Spectrophotometer (ISSW) in quantifying the concentration of refractory black carbon (BC) in snow samples. We find that the SP2 can be used to measure BC mass concentration in snow with substantially larger uncertainty (60 %) than for atmospheric sampling (<30 %). Achieving this level of accuracy requires careful assessment of nebulizer performance and SP2 calibration with consideration of the fact that BC in snow can exist in larger sizes than typically observed in the atmosphere. Once these issues are addressed, the SP2 is able to measure the size distribution and mass concentration of BC in the snow. Laboratory comparison of the SP2 and the ISSW revealed significant biases in the estimate of BC concentration from the ISSW when test samples contained dust or nonabsorbing particulates. These results suggest that current estimates of BC mass concentration in snow or ice formed from fallen snow using either the SP2 or the ISSW may be associated with significant underestimates of uncertainty.

Improved refrigeration techniques have lead to scientific discoveries such as superconductivity and Bose-Einstein condensation. Improved refrigeration techniques also enhance our quality of life. Semiconductor processing equipment and magnetic-resonance imaging machines incorporate mechanical coolers operating below 10 K. There is a pressing need for refrigeration techniques to reach even lower temperatures because many next-generation analytical and astronomical instruments will rely on sensors cooled to temperatures near 100 mK. Here we demonstrate a solid-state, on-chip refrigerator capable of reaching 100 mK based on the quantum-mechanical tunneling of electrons through normal metal-insulator-superconductor junctions. The cooling power and temperature reduction of our refrigerator are sufficient for practical applications and we have used it to cool bulk material that has no electrical connection to the refrigerating elements.

Invasive aquatic species introductions cause tremendous environmental and economic damage. Conservation and management efforts will benefit from rapid, inexpensive, and accurate on-site methods to detect harmful aquatic species to prevent their introduction and spread. Here, two technologies, environmental DNA (eDNA) sampling and Light Transmission Spectroscopy (LTS), were combined to address this need. Specifically, eDNA filtering and extraction methods were used to isolate DNA from: (1) lake water samples that were seeded with a microscopic fragment of five high-risk invasive species and (2) untreated samples from lakes infested with the invasive zebra mussel, Dreissena polymorpha, followed by polymerase chain reaction (PCR) amplification. LTS was then used to detect size shifts resulting from hybridization of PCR products with nanobeads covered with species-specific oligonucleotide probes. The results demonstrate that coupling eDNA sampling with LTS species detection can provide a sensitive and real-time solution for screening real-world water samples for invasive species.

We have studied electron tunneling in ultralow-capacitance silver particles sandwiched between artificial tunnel barriers. We have observed steps in the current-voltage characteristics of these systems with voltage widths of e/C (C being the capacitance of the particles), and associated current rises of e/RC. This represents the first observation of the so-called Coulomb staircase, expected for the charging of particles with extremely small capacitance by a discrete number of electrons.PACS numbers: 73.40. Gk, 36.40.+d Very recently, excitement has been generated by the realization that with currently developed materialspreparation techniques, it should be possible to observe the charging of metal particles by a small and countable number of electrons. Indeed, by employing recently developed techniques for the preparation of artificial electron tunnel barriers, we have performed tunneling studies of Ag particles sandwiched between these barriers in structures of the form metal/barrier/particles/ barrier/metal, wherein such effects have been observed. We discuss in this Letter tunneling measurements which reveal clear, periodic modulations of the dc and ac conductance as a function of voltage corresponding to the occupation of ultralow-capacitance silver particles by discrete numbers of electrons.Begun originally by Giaever and Zeller 1 to see whether superconductivity would persist in dimensionally restricted samples, the study of tunneling in small metal particles has been of continual interest because of the myriad outstanding questions regarding the nature of conductors on an ultrasmall scale. Recently, tunneling in small-particle and granular systems has been employed as a natural means of studying Coulomb and localization effects, which tend to be amplified in such systems. The subject has been approached from the standpoint of temperature and finite-frequency effects theoretically by Ho 2 and experimentally by Cavicchi and Silsbee 3 by means of tunnel-capacitor structures of the type originally described by Lambe and Jaklevic. 4 Transport measurements have also been made by Raven 5 in small-particle systems, and tunneling investigations have been performed by White, Dynes, and Garno 6 in granular materials, the latter in conjunction with the study of localization and interaction effects.The goal of the present work is the direct observation of the charging of particles by small, countable numbers of electrons. To accomplish this, we performed tunneling measurements of ultralow-capacitance (< 10 ~1 7 F) Ag particles wherein the charging voltage corresponding to a single electron, e/C, is in an easily measurable range (> 10" 2 V).The systems studied consist of structures containing a layer of isolated Ag particles sandwiched between welldefined artificial tunnel barriers. These systems were prepared by the layer-by-layer deposition of thin films as follows: base electrode/barrier/particles/barrier/counterelectrode. The barriers consist of sputter-deposited AI2O3 films in the 25-to 40-A thickness range. As ...

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