Biomedical subjects

Alvaro Hernández

Publications and source records attributed to Alvaro Hernández.

3 recordsLinked to original sources

PubMed2006

High reliability outdoor sonar prototype based on efficient signal coding.

Many mobile robots and autonomous vehicles designed for outdoor operation have incorporated ultrasonic sensors in their navigation systems, whose function is mainly to avoid possible collisions with very close obstacles. The use of these systems in more precise tasks requires signal encoding and the incorporation of pulse compression techniques that have already been used with success in the design of high-performance indoor sonars. However, the transmission of ultrasonic encoded signals outdoors entails a new challenge because of the effects of atmospheric turbulence. This phenomenon causes random fluctuations in the phase and amplitude of traveling acoustic waves, a fact that can make the encoded signal completely unrecognizable by its matched receiver. Atmospheric turbulence is investigated in this work, with the aim of determining the conditions under which it is possible to assure the reliable outdoor operation of an ultrasonic pulse compression system. As a result of this analysis, a novel sonar prototype based on complementary sequences coding is developed and experimentally tested. This encoding scheme provides the system with very useful additional features, namely, high robustness to noise, multi-mode operation capability (simultaneous emissions with minimum cross talk interference), and the possibility of applying an efficient detection algorithm that notably decreases the hardware resource requirements.

Data Compression↗

PubMed2005

The planarian Schmidtea mediterranea as a model for epigenetic germ cell specification: analysis of ESTs from the hermaphroditic strain.

Freshwater planarians have prodigious regenerative abilities that enable them to form complete organisms from tiny body fragments. This plasticity is also exhibited by the planarian germ cell lineage. Unlike many model organisms in which germ cells are specified by localized determinants, planarian germ cells appear to be specified epigenetically, arising postembryonically from stem cells. The planarian Schmidtea mediterranea is well suited for investigating the mechanisms underlying epigenetic germ cell specification. Two strains of S. mediterranea exist: a hermaphroditic strain that reproduces sexually and an asexual strain that reproduces by means of transverse fission. To date, expressed sequence tags (ESTs) have been generated only from the asexual strain. To develop molecular reagents for studying epigenetic germ cell specification, we have sequenced 27,161 ESTs from two developmental stages of the hermaphroditic strain of S. mediterranea; this collection of ESTs represents approximately 10,000 unique transcripts. blast analysis of the assembled ESTs showed that 66% share similarity to sequences in public databases. We annotated the assembled ESTs using Gene Ontology terms as well as conserved protein domains and organized them in a relational database. To validate experimentally the Gene Ontology annotations, we used whole-mount in situ hybridization to examine the expression patterns of transcripts assigned to the biological process "reproduction." Of the 53 genes in this category, 87% were expressed in the reproductive organs. In addition to its utility for studying germ cell development, this EST collection will be an important resource for annotating the planarian genome and studying this animal's amazing regenerative abilities.

Animals↗

PubMed2004

Ultrasonic ranging sensor using simultaneous emissions from different transducers.

In recent applications based on ultrasound, several ultrasonic transducers have been geometrically and electronically associated to constitute a global sensor. There are several different methods used to process the ultrasonic signals obtained from these transducers. In this work, multimode techniques using Golay complementary sequences are proposed for processing the ultrasonic signal. The system increases scan rate, precision, and reliability. It is also capable of echo discrimination, allowing simultaneous measurements to be made and detection of the same obstacle by different transducers without cross-talk problems. The real-time implementation of the algorithm is presented on a field-programmable gate array (FPGA) device.

Algorithms↗