Although role-based access control has become a preferred method to manage access control, it constitutes a significant effort to develop and maintain a role structure. Role engineering, the process of defining roles and assigning permissions and users to the roles, aims to define an accurate and complete set of roles using a variety of inputs. In this paper, we describe a unified approach to role engineering supporting a combination of different methodologies, and its partial implementation in the IBM Tivoli Role Modeling Assistant, a role engineering platform reflecting the dual importance of top-down and bottom-up data collection and analysis. Data, imported from multiple sources such as LDAP registries, human resource extracts in CSV format as well as from interviews with the organization's users and subject matter experts, can be browsed, filtered, and visualized. Roles can be created and edited manually or generated automatically from mining results.

The thermal dynamic behaviors of terahertz quantum cascade lasers are investigated using a spectrally matching terahertz quantum-well photodetector. The THz output power of a lasing device under a pulse excitation is found to decrease with time, which is attributed to the increase of active-region temperature. The measurements show that the duration of output lasing pulse ranges from a few microseconds up to 77 ¿s, depending on device bias and heat-sink temperature. A theoretical analysis based on a two-dimensional heat diffusion model is presented. The model calculates lasing quenching time based on an ¿average active-region temperature¿ criterion as well as a ¿reserve of gain¿ criterion. The best fit for quenching time is found when the vertical thermal conductivity in the quantum well region is two orders of magnitude lower than that of substrate. The measured lasing quenching time is in very good agreement with theoretical modeling calculated using both criteria.

In this letter, we report a near-infrared (NIR) optical upconverter consisting of an integrated InGaAs-InP heterojunction phototransistor (HPT) with an organic light-emitting diode (OLED), which converts 1.5-mu m IR light to visible light with a built-in electrical gain. The device was fabricated through direct tandem integration of an OLED with an inorganic InGaAs-InP HPT. Incoming 1.5-mu m optical radiation is absorbed by the HPT, generating an amplified photocurrent. The resultant photocurrent drives the OLED that emits at 545 nm. Upconversion is demonstrated at room temperature with a gain of 15 from the HPT and an overall external upconversion efficiency of 0.15 W/W.

An all photonic terahertz communication link operating at 3.8 THz using a quantum cascade laser and quantum well photodetector has been demonstrated. The link consists of a quantum cascade laser transmitter and a quantum well photodetector receiver. The link was used to transmit audio through 2 m of room air. Carrier strength at the photodetector was 100 times greater than the noise level measured...

We report on recent measurements on GaAs/AlGaAs THz quantum well infrared photodetectors (QWIPs), investigating linewidth broadening as function of doping level. Structures with 3% and 2% Al content in the barrier were grown using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Linewidth widening with increasing doping of the GaAs quantum well could be observed in the detection spectra. The observed shift of peak detection wavelength for different well dopings fits with values obtained from wavefunction calculations, taking into account many-particle effects, namely exchange and correlation energies and the effect of depolarization on the absorption. In addition, activation energies extracted from dark current measurements as function of device temperature are also in agreement with the calculations.

A near-infrared to visible light optical upconverter by the integration of an i-In0.53Ga0.47As/C60 junction and an organic light emitting diode is reported. This device shows the photovoltaic effect of an i-In0.53Ga0.47As/C60 heterojunction and potential application in a pixelless upconversion imaging device.

This paper presents our research and development efforts in realizing and perfecting organic/inorganic photon upconversion devices for wavelengths from near infrared (1.5 μm) region to visible light (green). The basic idea is to integrate an InGaAs/InP photodetector with an organic light emitting diode (OLED), connected in series. The detected photocurrent drives the OLED to emit visible light, thereby achieving the upconversion. A few approaches of integration methods and device designs have been tested.

A demonstration of a THz free space transmitter/receiver link using only 2 quantum well semiconductor devices is described. A GaAs/AlGaAs QCL operating at 3.8 THz was used to transmit music to a GaAs/AlGaAs QW detector thrugh an air pah of 2 meters.

This paper gives an overview on the design, fabrication, and characterization of quantum cascade detectors. They are tailorable infrared photodetectors based on intersubband transitions in semiconductor quantum wells that do not require an external bias voltage due to their asymmetric conduction band profile. They thus profit from favorable noise behavior, reduced thermal load, and simpler readout circuits. This was demonstrated at wavelengths from the near infrared at 2 mum to THz radiation at 87 mum using different semiconductor material systems.

We report on our development of both detectors and lasers in the terahertz (THz) region. For detection, we focus on the approach based on the extension of the celebrated quantum well infrared photodetectors (QWIPs); whereas the quantum cascade lasers (QCLs) provide the source. We show our preliminary demonstration of free space communication using our detectors and lasers. An all photonic THz communication link operating at 3.8 THz using a QCL and quantum well photodetector has been demonstrated. The link consists of a quantum cascade laser transmitter and a quantum well photodetector receiver. The link was used to transmit audio through two meters of room air. Carrier strength at the photodetector was 100 times above the noise level measured. THz free space communication may be of interest in satellite based systems.

The authors report on short-wavelength In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum cascade detectors (QCDs). At room temperature, one device detects at 505meV (2.46μm) with a responsivity of 2.57mA∕W, while a second QCD is sensitive at 580meV (2.14μm) with a responsivity of 0.32mA∕W.

Corporate decision makers have normally been disconnected from the details of the security management infrastructures of their organizations. The management of security resources has traditionally been the domain of a small group of skilled and technically savvy professionals, who report to the executive team. As threats become more prevalent, attackers get smarter and the infrastructure required to secure corporate assets become more complex, the communication gap between the decision makers and the implementers has widened. The risk of misinterpretation of corporate strategy into technical safe controls also increases with the above-mentioned trends. In this paper, we articulate a paradigm for managing enterprise security called the data centric security model (DCSM), which puts IT policy making in the hands of the corporate executives, so that security decisions can be directly executed without the diluting effect of interpretation at different levels of the Infrastructure and with the benefit of seeing direct correlation between business objective and security mechanism. Our articulation of the DCSM vision is a starting point for discussion and provides a rich platform for research into business-driven security management.

With the aim of increasing the efficiency of green and blue light-emitting diodes, we investigate the luminescence of InGaN/GaN quantum wells on structured GaN buffer layers.The peak emission wavelength of such systems depends among other factors on the In concentration, but the latter cannot be increased at will during growth of the quantum well structures, for stability reasons. However, it depends in turn on the buffer surface orientation, and therefore structuring the buffer before growth of the quantum wells can result in local variations of In concentration, and consequently peak emission wavelength.We present first results of local modification of emission wavelength, as shown by photo- and cathodoluminescence, and propose further experiments.

The authors report on an InP based photovoltaic quantum cascade detector operating at 16.5μm and using miniband-based vertical transport. This concept allowed the construction of a longitudinal optical phonon extraction stair with two rungs without touching on a high device resistance. At 10K, they observed a responsivity of 1.72mA∕W and a Johnson noise limited detectivity of 2.2×109 Jones. Altogether, this design resulted in detection at temperatures of up to 90K with a lower bandwidth limit of 200MHz imposed by the measurement setup.

We present two InP-based quantum cascade detectors (QCDs) in the mid-infrared wavelength range. Their narrow band detection spectra are centered at 5.3 and 9μm. A vertical intersubband transition followed by a carefully designed extraction cascade, which is adapted to the LO-phonon energy, leads to 10K responsivities R of 3.2 and 9.0mA∕W and background limited detectivities DBLIP* of 2×108 and 3×109 Jones, for the 5.3 and the 9μm devices, respectively. Detection has been observed up to device temperatures of 300K (RT), albeit reasonable performance is restricted to temperatures below 150K (5.3μm) and 70K (9μm). Designed for zero bias operation, QCDs do not produce any dark current and therefore do not suffer from dark current noise and capacitance saturation at long integration times, making them ideal devices for large focal plane arrays.