Orthogonal space-time block codes for free-space IM/DD optical links

Use of orthogonal space-time block codes (STBCs) with multiple transmitters and receivers can improve signal quality. However, in optical intensity modulated signals, output of the transmitter is non-negative and hence standard orthogonal STBC schemes need to be modified. A generalised framework for applying orthogonal STBCs for free-space IM/DD optical links is presented.

Stratospheric water vapor and climate: sensitivity to the representation in radiation codes

There has been considerable interest in the climate impact of trends in stratospheric water vapor (SWV). However, the representation of the radiative properties of water vapor under stratospheric conditions remains poorly constrained across different radiation codes. This study examines the sensitivity of a detailed line-by-line (LBL) code, a Malkmus narrow-band model and two broadband GCM radiation codes to a uniform perturbation in SWV in the longwave spectral region. The choice of sampling rate in wave number space (Δν) in the LBL code is shown to be important for calculations of the instantaneous change in heating rate (ΔQ) and the instantaneous longwave radiative forcing (ΔFtrop). ΔQ varies by up to 50% for values of Δν spanning 5 orders of magnitude, and ΔFtrop varies by up to 10%. In the three less detailed codes, ΔQ differs by up to 45% at 100 hPa and 50% at 1 hPa compared to a LBL calculation. This causes differences of up to 70% in the equilibrium fixed dynamical heating temperature change due to the SWV perturbation. The stratosphere-adjusted radiative forcing differs by up to 96% across the less detailed codes. The results highlight an important source of uncertainty in quantifying and modeling the links between SWV trends and climate.

Using QR codes to aid accessibility in a museum

Purpose – This paper describes visitors' reactions to using an Apple iPad or smartphone to follow trails in a museum by scanning QR codes and draws conclusions on the potential for this technology to help improve accessibility at low-cost. Design/methodology/approach – Activities were devised which involved visitors following trails around museum objects, each labelled with a QR code and symbolised text. Visitors scanned the QR codes using a mobile device which then showed more information about an object. Project-team members acted as participant-observers, engaging with visitors and noting how they used the system. Experiences from each activity fed into the design of the next. Findings – Some physical and technical problems with using QR codes can be overcome with the introduction of simple aids, particularly using movable object labels. A layered approach to information access is possible with the first layer comprising a label, the second a mobile-web enabled screen and the third choices of text, pictures, video and audio. Video was especially appealing to young people. The ability to repeatedly watch video or listen to audio seemed to be appreciated by visitors with learning disabilities. This approach can have low equipment-cost. However, maintaining the information behind labels and keeping-up with technological changes are on-going processes. Originality/value – Using QR codes on movable, symbolised object labels as part of a layered information system might help modestly-funded museums enhance their accessibility, particularly as visitors increasingly arrive with their own smartphones or tablets.