Estimation of Sparsity via Simple Measurements

We consider several related problems of estimating the 'sparsity' or number of nonzero elements $d$ in a length $n$ vector $\mathbf{x}$ by observing only $\mathbf{b} = M \odot \mathbf{x}$, where $M$ is a predesigned test matrix independent of $\mathbf{x}$, and the operation $\odot$ varies between problems. We aim to provide a $\Delta$-approximation of sparsity for some constant $\Delta$ with a minimal number of measurements (rows of $M$). This framework generalizes multiple problems, such as estimation of sparsity in group testing and compressed sensing. We use techniques from coding theory as well as probabilistic methods to show that $O(D \log D \log n)$ rows are sufficient when the operation $\odot$ is logical OR (i.e., group testing), and nearly this many are necessary, where $D$ is a known upper bound on $d$. When instead the operation $\odot$ is multiplication over $\mathbb{R}$ or a finite field $\mathbb{F}_q$, we show that respectively $\Theta(D)$ and $\Theta(D \log_q \frac{n}{D})$ measurements are necessary and sufficient.Comment: 13 pages; shortened version presented at ISIT 201

Studies on hip fracture patients : effects of nutrition and rehabilitation

Hip fracture in the elderly is a serious condition associated with increased mortality. Survivors experience an increase in morbidity and disability that affect their independence and quality of life; the outcome for patients with dementia is particularly poor. Many hip fracture patients have signs of malnutrition already on admission and this patient group has been shown to have a lower body mass index (BMI) than aged-matched controls. A catabolic state develops following hip fracture, characterized by loss of bone mineral density (BMD) and muscle mass. The combination of generalized loss of muscle mass, muscle strength and/or physical performance is known as sarcopenia, which impacts functionality and health- related quality of life. This thesis has three major aims: 1) to study the possible association between BMI, a potentially modifiable factor, and one-year mortality, as well as the ability to return to independent living following hip fracture; 2) to evaluate the effect of nutritional supplementation on bone mineral density (BMD), body composition, muscle strength and health-related quality of life (HRQoL) following hip fracture; and 3) to investigate factors of importance for preservation of ambulatory function and activities of daily living (ADL) following hip fracture in patients with cognitive impairment. Study I: A prospective study of 843 elderly patients with hip fracture, without severe cognitive impairment, who came from an independent living situation at the time of admission. The results show that overweight was associated with increased one-year survival and a greater likelihood of independent living one year post-fracture. Study II: A randomized controlled study in which 79 patients with hip fracture were randomized to one of three treatment groups. Six months of postoperative treatment with protein and energy-rich supplementation combined with orally administered bisphosphonate, calcium and vitamin D were shown to have a small additive effect on bone mineral density compared with bisphosphonate and calcium alone. Study III: A randomized controlled study of the same population as in study II. Postoperative treatment with protein and energy-rich supplementation did not prevent loss of lean mass following hip fracture. However, trends toward improved handgrip strength and HRQoL were observed following nutritional supplementation. Study IV: A prospective study of 246 patients with femoral neck fracture and cognitive impairment, but ambulant prior to fracture. In addition to ambulatory and ADL function prior to fracture, the results showed that discharge to rehabilitation facilities was associated with preserved ambulatory function and ADL skills at the 4-and 12 month follow-ups

To move ahead - the extension of a life-world

This licentiate thesis is a monography complemented with one published article: “Interactive Design – the desire for autonomous upright mobility: A longitudinal case study, Technology and Disability 19 (2007) 213-224”. My hope is that the combination of the monographic part (with its phenomenological tone, personified and situated), and the more unbarked “Technology and Disability” article (with its orientation towards the general rather than the personal aspects) will contribute to dialogues on different scientifical approaches. The overall purpose of this thesis is to develop new knowledge on child development under the conditions of SMA II. As I use a life-world phenomenological approach my first quest is to highlight and make explicit what appeared in Hanna’s life-world and how these experiences have contributed to her overall development. I also want to put forward how Hanna’s motility and mobility were supported, guided by what she expressed and strived for, in order to promote a healthy physical, psychological and social development. A special focus is on independent locomotion and how this was accomplished for Hanna. By using technology in a new way it was possible to enhance Hanna’s access to the world through the medium of her lived body, thus changing her life-world by widening her life-world horizon. The second quest of this licentiate thesis is to make this journey explicit

Yes we can - bidrage til at skabe ny vækst!

I DEFF undrer man sig højlydt over den skepsis, som forskningsbibliotekerne udviser over for den seneste DEFF-strategi. Hvorfor skulle bibliotekerne ikke kunne understøtte virksomhederne med support og services

Debugging the future: quality of life, academic success and student acceptability of assistive technology

Research has shown that integration of Assistive Technology (AT) in the educational environment is minimal but can offer life-changing benefits. My study explores the obstacles of AT and the relationship between acceptability of AT and student quality of life as well as individual self-reported academic success. I surveyed two existing groups of students at a regional comprehensive university. The first group is receiving assistance through instruction and tutoring services. The second group is receiving support to pursue future doctoral studies. Participants provided self-report of their academic strengths and challenges, acceptability of AT, and quality of life. I offered participants multiple opportunities to learn about and engage in different types of AT. Types of AT offered included: Read and Write Gold 10 (2013 Texthelp Ltd, 2013) Grammarly (Grammarly, Inc., 2013), and Dragon Naturally Speaking (Nuance Communications, Inc., 2012-2013). I predicted that higher self-reported academic challenges would increase acceptability towards AT and decrease self-reported quality of life. I also predicted that students with higher GPA would be less accepting to AT interventions. I found that there was no correlation between GPA and acceptability of AT or self-reported academic struggles and acceptability of AT. I did however find a significant negative correlation between quality of life and self-reported academic challenges

Algorithms to Exploit Data Sparsity

While data in the real world is very high-dimensional, it generally has some underlying structure; for instance, if we think of an image as a set of pixels with associated color values, most possible settings of color values correspond to something more like random noise than what we typically think of as a picture. With an appropriate transformation of basis, this underlying structure can often be converted into sparsity in data, giving an equivalent representation of the data where the magnitude is large in only a few directions relative to the ambient dimension. This motivates a variety of theoretical questions around designing algorithms that can exploit this data sparsity to achieve better performance than what would be possible naively, and in this thesis we tackle several such questions.We first examine the question of simply approximating the level of sparsity of a signal under several different measurement models, a natural first step if the sparsity is to be exploited by other algorithms. Second, we look at a particular sparse signal recovery problem called nonadaptive probabilistic group testing, and investigate the question of exactly how sparse the signal needs to be before the methods used for recovering sparse signals outperform those used for non-sparse signals. Third, we prove novel upper bounds on the number of measurements needed to recover a sparse signal in the universal one-bit compressed sensing model of sparse signal recovery. Fourth, we give some approximations of an information-theoretic quantity called the index coding rate of a network modeled by a graph, in the special case that the graph is sparse or otherwise highly structured. For each of the problems considered, we also discuss some remaining open questions and conjectures, as well as possible directions towards their solutions

Performances at an AIDS Memorial Quilt Display: An Ethnographic Study of Rehearsal

Several tentative research questions posed early in the study focused on the audience. The study of audience was later abandoned because it would not have been feasible for one researcher to conduct analyses of audiences while also observing performers. A study of these audiences would have been interesting because these were not a typical audience coming to a theatre for entertainment. These audiences were emotionally tied to the topic of the texts. Most of the audience members were highly knowledgeable about AIDS and related issues. The only audience analyses in this study were the directors\u27 and performers\u27 impressions of audience response obtained through interviews and the researcher\u27s own observations. The questions of the study became: what behaviors occurred during rehearsals, what were the performers\u27 initial impressions of the script, did these impressions change over time, how much initial knowledge did the performers have about AIDS and the AIDS Memorial Quilt, how well did the performers function as a group, and what ~ were the performers reactions to and perceptions of events at the quilt display

Seeing the World through a Camera Lens - Introducing the ‘Expert-Amateur’ Photographer

Through different blogs, social medias and apps people are sharing pictures like never before. Sales in expensive DSLR cameras have increased, and companies in the photo industry are providing customers with lessons to help them in their quest to become better photographers. From being just an object symbol of tourism it has evolved into becoming a lifestyle for many photography enthusiasts. This translates in a growing number of amateur photographers spending copious amounts of time and money on perfecting their skills and pursuing their passion. Although this trend has been a growing consumer practice for more than a decade, few researchers have focused on this field. The existing studies have mainly focused on either serious amateurs that are part of photo clubs or have reduced the field of photography into two groups: professionals and the rest. The analysis of the consumers interested in photography is more complex and cannot be limited to two groups. Hence, there is an existing research gap that this paper aims to fill. By combining insights gained through in-depth interviews from both amateurs and professionals with relevant theories from the field of consumer behaviour and sociology, we wish to better understand these consumers. This leads us to introduce the concept of ‘expert-amateur’ as a new way to define these highly engaged consumers and their practices. They are characterized by sharing similarities with both professionals (‘experts’) and everyday users ('amateurs’). Doing so we wish to shed some light on this developing consumer practice