Keyword field-free conjunctive keyword searches on encrypted data and extension for dynamic groups

We consider the following problem: a user stores encrypted documents on an untrusted server, and wishes to retrieve all documents containing some keywords without any loss of data confidentiality. Conjunctive keyword searches on encrypted data have been studied by numerous researchers over the past few years, and all existing schemes use keyword fields as compulsory information. This however is impractical for many applications. In this paper, we propose a scheme of keyword field-free conjunctive keyword searches on encrypted data, which affirmatively answers an open problem asked by Golle et al. at ACNS 2004. Furthermore, the proposed scheme is extended to the dynamic group setting. Security analysis of our constructions is given in the paper.

Modeling of protein signaling networks in clinical proteomics

Molecular interactions that underlie pathophysiological states are being elucidated using techniques that profile proteomicend points in cellular systems. Within the field of cancer research, protein interaction networks play pivotal roles in the establishment and maintenance of the hallmarks of malignancy, including cell division, invasion, and migration. Multiple complementary tools enable a multifaceted view of how signal protein pathway alterations contribute to pathophysiological states.One pivotal technique is signal pathway profiling of patient tissue specimens. This microanalysis technology provides a proteomic snapshot at one point in time of cells directly procured from the native context of a tumor micro environment. To study the adaptive patterns of signal pathway events over time, before and after experimental therapy, it is necessary to obtain biopsies from patients before, during, and after therapy. A complementary approach is the profiling of cultured cell lines with and without treatment. Cultured cell models provide the opportunity to study short-term signal changes occurring over minutes to hours. Through this type of system, the effects of particular pharmacological agents may be used to test the effects of signal pathway inhibition or activation on multiple endpoints within a pathway. The complexity of the data generated has necessitated the development of mathematical models for optimal interpretation of interrelated signaling pathways. In combination,clinical proteomic biopsy profiling, tissue culture proteomic profiling, and mathematical modeling synergistically enable a deeper understanding of how protein associations lead to disease states and present new insights into the design of therapeutic regimens.

Dispersion of corona ions downwind from a high-voltage power line

Corona discharge is responsible for the small ions found near overhead power lines, and these are capable of modifying the ambient electrical environment such as the dc electric field at ground level (Fews, Wilding et al. 2002). Once produced, small ions quickly attach to aerosol particles in the air, producing ‘large ions’ which are roughly 1 nm to 1 µm in diameter. However, very few studies have reported measurements of ions produced by power lines and its impact on particle charge concentrations. In this present study, the measurements were conducted as a function of normal downwind distance from a 275kV power line for investigating the effect of corona ions on air ions, aerosol particle charge concentration and dc e-filed.

Air ion concentrations under overhead power lines

Corona discharge is responsible for the flux of small ions from overhead power lines, and is capable of modifying the ambient electrical environment, such as the air ion concentrations at ground level. Once produced, small ions quickly attach to aerosol particles in the air, producing ‘large ions’, approximately 1 nm to 1 µm in diameter. However, very few studies have measured air ion concentrations directly near high voltage transmission lines. The present study involved the simultaneously measurement of small ion concentration and net large ion concentration using air ion counters and an aerosol electrometer at four power line sites. Both positive and negative small ion concentration (<1.6nm), net large ion concentration (2nm-5μm) and particle number concentration (10nm-2μm) were measured using air ion counters and an aerosol electrometer at four power line sites. Measurements at sites 1 and 2 were conducted at both upwind and downwind sides. The results showed that total ion concentrations on the downwind side were 3-5 times higher than on the upwind side, while particle number concentrations did not show a significant difference. This result also shows that a large number of ions were emitted from the power lines at sites 1 and 2. Furthermore, both positive and negative ions were observed at different power line sites. Dominant positive ions were observed at site 1, with a concentration of 4.4 x 103 ions cm-3, which was 10 times higher than on the upwind side. Contrary to site 1, sites 2 to 4 showed negative ion emissions, with concentrations of -1.2 x 103, -460 and -410 ions cm-3, respectively. These values were higher than the background urban negative ion concentration of 400 cm-3. At site 1 and site 2, the net ion concentration and net particle charge concentration on downwind side of the lines showed same polarities. Further investigations were also conducted into the correlation between net ion concentration and net charge particle concentration 20 m downwind of the power lines at site 2. The two parameters showed a correlation coefficient of 0.72, indicating that a substantial number of ions could attach to particles and affect the particle charge status within a short distance from the source.

Charged particles produced by corona emission from an overhead high voltage powerline

High voltage powerlines may give rise to corona breakdown, resulting in the release of large concentrations of charged ions into the surrounding environment. These ions quickly attach to aerosols and the resulting charged particles are carried by prevalent winds. This paper describes a study carried out at a site near an overhead double circuit ac transmission voltage powerline to investigate factors that control the rate at which charged particles are produced, and to determine the total particle number concentrations, total particle charge concentrations and vertical dc electric fields in the proximity of the line. Measured mean values of these three parameters at a perpendicular distance of 50m from the line were 1.8 x 103 particle cm-3, 518 ions cm3 and 520 V m-1 respectively. The net electric charge was positive and the electric field was directed downwards. These parameters were correlated with each other and monitored at four different distances from the line. Effects of meteorological parameters such as wind speed and wind direction were also investigated.

Can estimates of antimalarial efficacy from field studies be improved?

Monitoring therapeutic efficacy of antimalarial drugs is important because treatment failure rates are the primary basis for changing antimalarial treatment policy. An important aspect of efficacy studies is the use of PCR genotyping to distinguish recrudescent from new infections. The conclusions reached using this technique might be misleading if there is insufficient parasite diversity or a non-uniform haplotype frequency distribution in the study area. Statistical techniques can be used to overcome this problem, but only when data describing the haplotype frequency distribution are available. Therefore, assessing haplotype frequency and distribution should form an integral part of all studies investigating the therapeutic efficacy of antimalarial treatment regimes.

Field-effect transistors based on self-organized molecular nanostripes

Charge transport properties in organic semiconductors depend strongly on molecular order. Here we demonstrate field-effect transistors where drain current flows through a precisely defined array of nanostripes made of crystalline and highly ordered molecules. The molecular stripes are fabricated across the channel of the transistor by a stamp-assisted deposition of the molecular semiconductors from a solution. As the solvent evaporates, the capillary forces drive the solution to form menisci under the stamp protrusions. The solute precipitates only in the regions where the solution is confined by the menisci once the critical concentration is reached and self-organizes into molecularly ordered stripes 100-200 nm wide and a few monolayers high. The charge mobility measured along the stripes is 2 orders of magnitude larger than the values measured for spin-coated thin films.

Band gap tunable N-type molecules for organic field effect transistors

A series of four novel n-type molecules has been synthesized. Unlike previous approaches, the end group of these molecules was fixed and the molecular core was varied. The resulting materials were thoroughly analyzed. Electronic properties were derived from photoemission spectroscopy, optical properties were derived with the help of optical spectroscopy, and the structure of thin films on Au(111) was derived by scanning tunneling microscopy (STM). In addition, prototypical organic field-effect transistors (OFETs) (forming n-channels in OFETs) have been fabricated and tested. The correlation between the device performance of the respective OFETs (i.e., electron mobility) and their electronic as well as structural properties was investigated. It turned out that a combination of beneficial electronic and structural properties provides the best results. These findings are important for the design of new materials for future device applications.

Charge carrier velocity distributions in high mobility polymer field-effect transistors

In this letter, the velocity distributions of charge carriers in high-mobility polymer thin-film transistors (TFTs) with a diketopyrrolopyrrole- naphthalene copolymer (PDPP-TNT) semiconductor active layer are reported. The velocity distributions are found to be strongly dependent on measurement temperatures as well as annealing conditions. Considerable inhomogeneity is evident at low measurement temperatures and for low annealing temperatures. Such transient transport measurements can provide additional information about charge carrier transport in TFTs which are unavailable using steady-state transport measurements.

Solution-processed dual-gate polymer field-effect transistors for display applications

We describe the advantages of dual-gate thin-film transistors (TFTs) for display applications. We show that in TFTs with active semiconductor layers composed of diketopyrrolopyrrole-naphthalene copolymer, the on-current is increased, the off-current is reduced, and the sub-threshold swing is improved compared to single-gate devices. Charge transport measurements in steady-state and under non-quasi-static conditions reveal the reasons for this improved performance. We show that in dual-gate devices, a much smaller fraction of charge carriers move in slow trap states. We also compare the activation energies for charge transport in the top-gate and bottom-gate configurations.

Characteristics of high-performance ambipolar organic field-effect transistors based on a diketopyrrolopyrrole-benzothiadiazole copolymer

In this paper, we report the device characteristics of ambipolar thin-film transistors (TFTs) based on a diketopyrrolopyrrole-benzothiadiazole copolymer. This polymer semiconductor exhibits the largest comparable electron and hole mobility values in a single organic semiconductor. The key to realizing such high mobility values, which are $0.5&cm}{2}/\hbox{V}̇\hbox{s, is molecular design, i.e., the use of suitable surface treatments of the source/drain contact electrodes and device architectures, particularly top-gate configurations. The subthreshold characteristics of the TFT devices are greatly improved by the use of dual-gate device geometry. We also report the first measurement of the velocity distribution of electron and hole velocities in an ambipolar organic semiconductor.

Electrical characteristics of lateral heterostructure organic field-effect bipolar transistors

We describe and discuss the unique electrical characteristics of an organic field-effect transistor in which the active layer consists of a type II lateral heterojunction located approximately midway between the source and drain. The two active semiconductors on either side of the junction transport only one carrier type each, with the other becoming trapped, which leads to devices that operate in only the steady state when there is balanced electron and hole injections from the drain and source. We describe the unique transfer characteristics of such devices in two material systems.

A study of the effects metal residues in poly(9,9-dioctylfluorene) have on field-effect transistor device characteristics

The amount of metal residues from organometallic reagents used in preparation of poly(9,9-dioctylfluorene) by palladium catalysed Suzuki and nickel-induced Yamamoto polycondensations have been determined, and their effect upon the behaviour of the polymer in field-effect transistors (FETs) has been measured. The metal levels from material polymerised by Suzuki method were found to be much higher than from that made by the Yamamoto procedure. Simple treatment of the polymers with suitable metal trapping reagents lowered the metal levels significantly, with EDTA giving best results for nickel and triphenylphosphine for palladium. Comparison of the behaviour of FETs using polyfluorenes with varying levels of metal contamination, showed that the metal residues have little effect upon the mobility values, but often affect the degree of hysteresis, possibly acting as charge traps. Satisfactory device performances were obtained from polymer with palladium levels of 2000 μg/g suggesting that complete removal of metal residues may not be necessary for satisfactory device performance.

Synthesis, characterization and organic field effect transistor performance of a diketopyrrolopyrrole-fluorenone copolymer

A diketopyrrolopyrrole (DPP) with fluorenone (FN) based low band gap alternating copolymer (PDPPT-alt-FN) has been synthesized via Suzuki coupling. PDPPT-alt-FN exhibits a deep HOMO level with a lower band gap. Fabricated organic thin film transistors using PDPPT-alt-FN as a channel semiconductor show p-channel behaviour with the highest hole mobility of 0.083 cm2 V-1 s-1 measured in air.

A fluorenone based low band gap solution processable copolymer for air stable and high mobility organic field effect transistors

A fluorenone based alternating copolymer (PFN-DPPF) with a furan based fused aromatic moiety has been designed and synthesized. PFN-DPPF exhibits a small band gap with a lower HOMO value. Testing this polymer semiconductor as the active layer in organic thin-film transistors results in hole mobilities as high as 0.15 cm2 V-1 s-1 in air.