title: Electrical Conductivity of Brain Cortex Slices in Seizing and Non-seizing States

authors: Elbohouty, Maher

subjects: Electrical Conductivity

abstract: The electrical conductivity of thin living slices of mouse cerebral cortex is measured. Two only out of fifteen different attempting ways were effective. I have successfully measured the electrical conductivity of mouse brain cortex in seizing and non-seizing conditions. The first successful approach is called 	the van der Pauw method, where four silver-silver chloride cylindrical wire electrodes were immersed in full length at the corners of the sample. The second is a one-dimensional technique where two flat electrodes were placed on either face of the 400 micrometer thick samples.

In both methods the electrodes were connected to an Agilent E4980A impedance monitor. The conductivity at 10 kHz of each sample was calculated based on measurements of injected current and potential difference between electrodes. Both approaches were validated by measuring electrical conductivities of known solutions. There were two main challenges: the small size of the sample and keeping it alive. I overcame these challenges by suitable electrodes and fast measuring equipment (Agilent E4980A LCR meter). For the one-dimensional technique I also measured the conductivity across the frequency range 20 Hz to 2 MHz.

The results consistently show the mean conductivity of seizing brain tissue is significantly lower than that of non-seizing tissue at 10 kHz. Also, the conductivity of seizing slices is lower than the conductivity of non-seizing slices over the frequency range 20 Hz to 2 MHz. 

These results suggest a link between electrical conductivity and seizure activity. I have not investigated the causes of these differences but explanations consistent with the literature are a change in chemical environment during seizure or a reduction in gap junction connectivity.

text: Electrical Conductivity of Brain Cortex Slices in Seizing and Non-seizing States The electrical conductivity of thin living slices of mouse cerebral cortex is measured. Two only out of fifteen different attempting ways were effective. I have successfully measured the electrical conductivity of mouse brain cortex in seizing and non-seizing conditions. The first successful approach is called 	the van der Pauw method, where four silver-silver chloride cylindrical wire electrodes were immersed in full length at the corners of the sample. The second is a one-dimensional technique where two flat electrodes were placed on either face of the 400 micrometer thick samples.

In both methods the electrodes were connected to an Agilent E4980A impedance monitor. The conductivity at 10 kHz of each sample was calculated based on measurements of injected current and potential difference between electrodes. Both approaches were validated by measuring electrical conductivities of known solutions. There were two main challenges: the small size of the sample and keeping it alive. I overcame these challenges by suitable electrodes and fast measuring equipment (Agilent E4980A LCR meter). For the one-dimensional technique I also measured the conductivity across the frequency range 20 Hz to 2 MHz.

The results consistently show the mean conductivity of seizing brain tissue is significantly lower than that of non-seizing tissue at 10 kHz. Also, the conductivity of seizing slices is lower than the conductivity of non-seizing slices over the frequency range 20 Hz to 2 MHz. 

These results suggest a link between electrical conductivity and seizure activity. I have not investigated the causes of these differences but explanations consistent with the literature are a change in chemical environment during seizure or a reduction in gap junction connectivity.

year: 2013

title: The impact of router outages on the AS-level internet

authors: Luckie, Matthew John

subjects: computer science

abstract: We propose and evaluate a new metric for understanding the dependence of the AS-level Internet on individual routers. Whereas prior work uses large volumes of reachability probes to infer outages, we design an efficient active probing technique that directly and unambiguously reveals router restarts. We use our technique to survey 149,560 routers across the Internet for 2.5 years. 59,175 of the surveyed routers (40%) experience at least one reboot, and we quantify the resulting impact of each router outage on global IPv4 and IPv6 BGP reachability.

Our technique complements existing data and control plane outage analysis methods by providing a causal link from BGP reachability failures to the responsible router(s) and multi-homing configurations. While we found the Internet core to be largely robust, we identified specific routers that were single points of failure for the prefixes they advertised. In total, 2,385 routers -- 4.0% of the routers that restarted over the course of 2.5 years of probing -- were single points of failure for 3,396 IPv6 prefixes announced by 1,708 ASes. We inferred 59% of these routers were the customer-edge border router. 2,374 (70%) of the withdrawn prefixes were not covered by a less specific prefix, so 1,726 routers (2.9%) of those that restarted were single points of failure for at least one network. However, a covering route did not imply reachability during a router outage, as no previously-responsive address in a withdrawn more specific prefix responded during a one-week sample. We validate our reboot and single point of failure inference techniques with four networks, finding no false positive or false negative reboots, but find some false negatives in our single point of failure inferences.

text: The impact of router outages on the AS-level internet We propose and evaluate a new metric for understanding the dependence of the AS-level Internet on individual routers. Whereas prior work uses large volumes of reachability probes to infer outages, we design an efficient active probing technique that directly and unambiguously reveals router restarts. We use our technique to survey 149,560 routers across the Internet for 2.5 years. 59,175 of the surveyed routers (40%) experience at least one reboot, and we quantify the resulting impact of each router outage on global IPv4 and IPv6 BGP reachability.

Our technique complements existing data and control plane outage analysis methods by providing a causal link from BGP reachability failures to the responsible router(s) and multi-homing configurations. While we found the Internet core to be largely robust, we identified specific routers that were single points of failure for the prefixes they advertised. In total, 2,385 routers -- 4.0% of the routers that restarted over the course of 2.5 years of probing -- were single points of failure for 3,396 IPv6 prefixes announced by 1,708 ASes. We inferred 59% of these routers were the customer-edge border router. 2,374 (70%) of the withdrawn prefixes were not covered by a less specific prefix, so 1,726 routers (2.9%) of those that restarted were single points of failure for at least one network. However, a covering route did not imply reachability during a router outage, as no previously-responsive address in a withdrawn more specific prefix responded during a one-week sample. We validate our reboot and single point of failure inference techniques with four networks, finding no false positive or false negative reboots, but find some false negatives in our single point of failure inferences.

year: 2017

title: Patient-reported diagnostic intervals to colorectal cancer diagnosis in the Midland region of New Zealand: a prospective cohort study

authors: Blackmore, Tania Louise

subjects: Science & Technology

abstract: Background and objectives
New Zealand (NZ) has high rates of colorectal cancer (CRC) but low rates of early detection. The majority of CRC is diagnosed through general practice, where lengthy diagnostic intervals are common. We investigated factors contributing to diagnostic delay in a cohort of patients newly diagnosed with CRC.

Methods
Patients were recruited from the Midland region and interviewed about their diagnostic experience using a questionnaire based on a modified Model of Pathways to Treatment framework and SYMPTOM questionnaire. Descriptive statistics were used to describe the population characteristics. Chi-square analysis and logistic regression were used to analyse factors influencing diagnostic intervals.

Results
Data from 176 patients were analysed, of which 65 (36.9%) experienced a general practitioner (GP) diagnostic interval of >120 days and 96 (54.5%) experienced a total diagnostic interval (TDI) > 120 days. Patients reporting rectal bleeding were less likely to experience a long TDI (odds ratio [OR] 0.34, 95% confidence interval [CI]: 0.14–0.78) and appraisal/help-seeking interval (OR, 0.19, 95% CI: 0.06–0.59). Patients <60 were more likely to report a longer appraisal/help-seeking interval (OR, 3.32, 95% CI: 1.17–9.46). Female (OR, 2.19, 95% CI: 1.08–4.44) and Māori patients (OR, 3.18, 95% CI: 1.04–9.78) were more likely to experience a long GP diagnostic interval.

Conclusion
NZ patients with CRC can experience long diagnostic intervals, attributed to patient and health system factors. Young patients, Māori, females, and patients experiencing change of bowel habit may be at particular risk. We need to increase symptom awareness of CRC for patients and GPs. Concentrated efforts are needed to ensure equity for Māori in access to screening, diagnostics, and treatment.

text: Patient-reported diagnostic intervals to colorectal cancer diagnosis in the Midland region of New Zealand: a prospective cohort study Background and objectives
New Zealand (NZ) has high rates of colorectal cancer (CRC) but low rates of early detection. The majority of CRC is diagnosed through general practice, where lengthy diagnostic intervals are common. We investigated factors contributing to diagnostic delay in a cohort of patients newly diagnosed with CRC.

Methods
Patients were recruited from the Midland region and interviewed about their diagnostic experience using a questionnaire based on a modified Model of Pathways to Treatment framework and SYMPTOM questionnaire. Descriptive statistics were used to describe the population characteristics. Chi-square analysis and logistic regression were used to analyse factors influencing diagnostic intervals.

Results
Data from 176 patients were analysed, of which 65 (36.9%) experienced a general practitioner (GP) diagnostic interval of >120 days and 96 (54.5%) experienced a total diagnostic interval (TDI) > 120 days. Patients reporting rectal bleeding were less likely to experience a long TDI (odds ratio [OR] 0.34, 95% confidence interval [CI]: 0.14–0.78) and appraisal/help-seeking interval (OR, 0.19, 95% CI: 0.06–0.59). Patients <60 were more likely to report a longer appraisal/help-seeking interval (OR, 3.32, 95% CI: 1.17–9.46). Female (OR, 2.19, 95% CI: 1.08–4.44) and Māori patients (OR, 3.18, 95% CI: 1.04–9.78) were more likely to experience a long GP diagnostic interval.

Conclusion
NZ patients with CRC can experience long diagnostic intervals, attributed to patient and health system factors. Young patients, Māori, females, and patients experiencing change of bowel habit may be at particular risk. We need to increase symptom awareness of CRC for patients and GPs. Concentrated efforts are needed to ensure equity for Māori in access to screening, diagnostics, and treatment.

year: 2021